net: hso: fix module unloading

net: hso: fix module unloading

keep tty driver until usb driver is unregistered
rmmod hso
produces traces like this without that:

[40261.645904] usb 2-2: new high-speed USB device number 2 using ehci-omap
[40261.854644] usb 2-2: New USB device found, idVendor=0af0, idProduct=8800
[40261.862609] usb 2-2: New USB device strings: Mfr=3, Product=2, SerialNumber=0
[40261.872772] usb 2-2: Product: Globetrotter HSUPA Modem
[40261.880279] usb 2-2: Manufacturer: Option N.V.
[40262.021270] hso 2-2:1.5: Not our interface
[40265.556945] hso: unloaded
[40265.559875] usbcore: deregistering interface driver hso
[40265.595947] Unable to handle kernel NULL pointer dereference at virtual address 00000033
[40265.604522] pgd = ecb14000
[40265.611877] [00000033] *pgd=00000000
[40265.617034] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
[40265.622650] Modules linked in: hso(-) bnep bluetooth ipv6 arc4 twl4030_madc_hwmon wl18xx wlcore mac80211 cfg80211 snd_soc_simple_card snd_soc_simple_card_utils snd_soc_omap_twl4030 snd_soc_gtm601 generic_adc_battery extcon_gpio omap3_isp videobuf2_dma_contig videobuf2_memops wlcore_sdio videobuf2_v4l2 videobuf2_core ov9650 bmp280_i2c v4l2_common bmp280 bmg160_i2c bmg160_core at24 nvmem_core videodev bmc150_accel_i2c bmc150_magn_i2c media bmc150_accel_core tsc2007 bmc150_magn leds_tca6507 bno055 snd_soc_omap_mcbsp industrialio_triggered_buffer snd_soc_omap kfifo_buf snd_pcm_dmaengine gpio_twl4030 snd_soc_twl4030 twl4030_vibra twl4030_madc wwan_on_off ehci_omap pwm_bl pwm_omap_dmtimer panel_tpo_td028ttec1 encoder_opa362 connector_analog_tv omapdrm drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect
[40265.698211]  sysimgblt fb_sys_fops cfbcopyarea drm omapdss usb_f_ecm g_ether usb_f_rndis u_ether libcomposite configfs omap2430 phy_twl4030_usb musb_hdrc twl4030_charger industrialio w2sg0004 twl4030_pwrbutton bq27xxx_battery w1_bq27000 omap_hdq [last unloaded: hso]
[40265.723175] CPU: 0 PID: 2701 Comm: rmmod Not tainted 4.11.0-rc6-letux+ #6
[40265.730346] Hardware name: Generic OMAP36xx (Flattened Device Tree)
[40265.736938] task: ecb81100 task.stack: ecb82000
[40265.741729] PC is at cdev_del+0xc/0x2c
[40265.745666] LR is at tty_unregister_device+0x40/0x50
[40265.750915] pc : [<c027472c>]    lr : [<c04b3ecc>]    psr: 600b0113
sp : ecb83ea8  ip : eca4f898  fp : 00000000
[40265.763000] r10: 00000000  r9 : 00000000  r8 : 00000001
[40265.768493] r7 : eca4f800  r6 : 00000003  r5 : 00000000  r4 : ffffffff
[40265.775360] r3 : c1458d54  r2 : 00000000  r1 : 00000004  r0 : ffffffff
[40265.782257] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[40265.789764] Control: 10c5387d  Table: acb14019  DAC: 00000051
[40265.795806] Process rmmod (pid: 2701, stack limit = 0xecb82218)
[40265.802062] Stack: (0xecb83ea8 to 0xecb84000)
[40265.806640] 3ea0:                   ec9e8100 c04b3ecc bf737378 ed5b7c00 00000003 bf7327ec
[40265.815277] 3ec0: eca4f800 00000000 ec9fd800 eca4f800 bf737070 bf7328bc eca4f820 c05a9a04
[40265.823883] 3ee0: eca4f820 00000000 00000001 eca4f820 ec9fd870 bf737070 eca4f854 ec9fd8a4
[40265.832519] 3f00: ecb82000 00000000 00000000 c04e6960 eca4f820 bf737070 bf737048 00000081
[40265.841125] 3f20: c01071e4 c04e6a60 ecb81100 bf737070 bf737070 c04e5d94 bf737020 c05a8f88
[40265.849731] 3f40: bf737100 00000800 7f5fa254 00000081 c01071e4 c01c4afc 00000000 006f7368
[40265.858367] 3f60: ecb815f4 00000000 c0cac9c4 c01071e4 ecb82000 00000000 00000000 c01512f4
[40265.866973] 3f80: ed5b3200 c01071e4 7f5fa220 7f5fa220 bea78ec9 0010711c 7f5fa220 7f5fa220
[40265.875579] 3fa0: bea78ec9 c0107040 7f5fa220 7f5fa220 7f5fa254 00000800 dd35b800 dd35b800
[40265.884216] 3fc0: 7f5fa220 7f5fa220 bea78ec9 00000081 bea78dcc 00000000 bea78bd8 00000000
[40265.892822] 3fe0: b6f70521 bea78b6c 7f5dd613 b6f70526 80070030 7f5fa254 ffffffff ffffffff
[40265.901458] [<c027472c>] (cdev_del) from [<c04b3ecc>] (tty_unregister_device+0x40/0x50)
[40265.909942] [<c04b3ecc>] (tty_unregister_device) from [<bf7327ec>] (hso_free_interface+0x80/0x144 [hso])
[40265.919982] [<bf7327ec>] (hso_free_interface [hso]) from [<bf7328bc>] (hso_disconnect+0xc/0x18 [hso])
[40265.929718] [<bf7328bc>] (hso_disconnect [hso]) from [<c05a9a04>] (usb_unbind_interface+0x84/0x200)
[40265.939239] [<c05a9a04>] (usb_unbind_interface) from [<c04e6960>] (device_release_driver_internal+0x138/0x1cc)
[40265.949798] [<c04e6960>] (device_release_driver_internal) from [<c04e6a60>] (driver_detach+0x60/0x6c)
[40265.959503] [<c04e6a60>] (driver_detach) from [<c04e5d94>] (bus_remove_driver+0x64/0x8c)
[40265.968017] [<c04e5d94>] (bus_remove_driver) from [<c05a8f88>] (usb_deregister+0x5c/0xb8)
[40265.976654] [<c05a8f88>] (usb_deregister) from [<c01c4afc>] (SyS_delete_module+0x160/0x1dc)
[40265.985443] [<c01c4afc>] (SyS_delete_module) from [<c0107040>] (ret_fast_syscall+0x0/0x1c)
[40265.994171] Code: c1458d54 e59f3020 e92d4010 e1a04000 (e5941034)
[40266.016693] ---[ end trace 9d5ac43c7e41075c ]---

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>