mcb: Implement bus->dev.release callback

mcb: Implement bus->dev.release callback

The mcb_bus structure previously was released in mcb_release_bus. This lead to
the following warning on module unload:

------------[ cut here ]------------
WARNING: CPU: 1 PID: 2032 at drivers/base/core.c:251 device_release+0x73/0x90
Device 'mcb:0' does not have a release() function, it is broken and must be fixed.
Modules linked in: men_z135_uart mcb_pci(-) mcb
CPU: 1 PID: 2032 Comm: rmmod Not tainted 4.6.0-rc4+ #3
Hardware name: N/A N/A/COMe-mBTi10, BIOS MVV1R921 X64 10/14/2015
 00000286 00000286 c0117de4 c12d6f16 c0117e2c c18be0d3 c0117dfc c104f6e1
 000000fb f5ccbe08 f5ccbe00 f5c64600 c0117e18 c104f728 00000009 00000000
 c0117e10 c18db674 c0117e2c c0117e3c c13ce5c3 c18be0d3 000000fb c18db674
Call Trace:
 [<c12d6f16>] dump_stack+0x47/0x61
 [<c104f6e1>] __warn+0xc1/0xe0
 [<c104f728>] warn_slowpath_fmt+0x28/0x30
 [<c13ce5c3>] device_release+0x73/0x90
 [<c12d92e4>] kobject_release+0x34/0x80
 [<c12d929d>] ? kobject_del+0x2d/0x40
 [<c12d9205>] kobject_put+0x25/0x50
 [<c13ce77f>] put_device+0xf/0x20
 [<c13d114b>] klist_devices_put+0xb/0x10
 [<c1752673>] klist_next+0x73/0xf0
 [<c13d1140>] ? unbind_store+0x100/0x100
 [<f8a23370>] ? mcb_bus_add_devices+0x30/0x30 [mcb]
 [<c13d0a81>] bus_for_each_dev+0x51/0x80
 [<f8a23319>] mcb_release_bus+0x19/0x40 [mcb]
 [<f8a23370>] ? mcb_bus_add_devices+0x30/0x30 [mcb]
 [<f8a2b033>] mcb_pci_remove+0x13/0x20 [mcb_pci]
 [<c130d358>] pci_device_remove+0x28/0xb0
 [<c13d201b>] __device_release_driver+0x7b/0x110
 [<c13d2847>] driver_detach+0x87/0x90
 [<c13d1b9b>] bus_remove_driver+0x3b/0x80
 [<c13d2ed0>] driver_unregister+0x20/0x50
 [<c130be53>] pci_unregister_driver+0x13/0x60
 [<f8a2b1f4>] mcb_pci_driver_exit+0xd/0xf [mcb_pci]
 [<c10be588>] SyS_delete_module+0x138/0x200
 [<c1159208>] ? ____fput+0x8/0x10
 [<c1068054>] ? task_work_run+0x74/0x90
 [<c1001879>] do_fast_syscall_32+0x69/0x120
 [<c1757597>] sysenter_past_esp+0x40/0x6a
---[ end trace 1ed34c2aa3019875 ]---

Release a mcb_bus' memory on the device's release callback, to avoid above
warning.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reported-by: Andreas Werner <andreas.werner@men.de>
Tested-by: Andreas Werner <andreas.werner@men.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>