pinctrl: at91: fix null pointer dereference

pinctrl: at91: fix null pointer dereference

Not all gpio banks are necessarily enabled, in the current code this can
lead to null pointer dereferences.

[   51.130000] Unable to handle kernel NULL pointer dereference at virtual address 00000058
[   51.130000] pgd = dee04000
[   51.130000] [00000058] *pgd=3f66d831, *pte=00000000, *ppte=00000000
[   51.140000] Internal error: Oops: 17 [#1] ARM
[   51.140000] Modules linked in:
[   51.140000] CPU: 0 PID: 1664 Comm: cat Not tainted 4.1.1+ #6
[   51.140000] Hardware name: Atmel SAMA5
[   51.140000] task: df6dd880 ti: dec60000 task.ti: dec60000
[   51.140000] PC is at at91_pinconf_get+0xb4/0x200
[   51.140000] LR is at at91_pinconf_get+0xb4/0x200
[   51.140000] pc : [<c01e71a0>]    lr : [<c01e71a0>]    psr: 600f0013
sp : dec61e48  ip : 600f0013  fp : df522538
[   51.140000] r10: df52250c  r9 : 00000058  r8 : 00000068
[   51.140000] r7 : 00000000  r6 : df53c910  r5 : 00000000  r4 : dec61e7c
[   51.140000] r3 : 00000000  r2 : c06746d4  r1 : 00000000  r0 : 00000003
[   51.140000] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
[   51.140000] Control: 10c53c7d  Table: 3ee04059  DAC: 00000015
[   51.140000] Process cat (pid: 1664, stack limit = 0xdec60208)
[   51.140000] Stack: (0xdec61e48 to 0xdec62000)
[   51.140000] 1e40:                   00000358 00000000 df522500 ded15f80 c05a9d08 ded15f80
[   51.140000] 1e60: 0000048c 00000061 df522500 ded15f80 c05a9d08 c01e7304 ded15f80 00000000
[   51.140000] 1e80: c01e6008 00000060 0000048c c01e6034 c01e5f6c ded15f80 dec61ec0 00000000
[   51.140000] 1ea0: 00020000 ded6f280 dec61f80 00000001 00000001 c00ae0b8 b6e80000 ded15fb0
[   51.140000] 1ec0: 00000000 00000000 df4bc974 00000055 00000800 ded6f280 b6e80000 ded6f280
[   51.140000] 1ee0: ded6f280 00020000 b6e80000 00000000 00020000 c0090dec c0671e1c dec61fb0
[   51.140000] 1f00: b6f8b510 00000001 00004201 c000924c 00000000 00000003 00000003 00000000
[   51.140000] 1f20: df4bc940 00022000 00000022 c066e188 b6e7f000 c00836f4 000b6e7f ded6f280
[   51.140000] 1f40: ded6f280 b6e80000 dec61f80 ded6f280 00020000 c0091508 00000000 00000003
[   51.140000] 1f60: 00022000 00000000 00000000 ded6f280 ded6f280 00020000 b6e80000 c0091d9c
[   51.140000] 1f80: 00000000 00000000 ffffffff 00020000 00020000 b6e80000 00000003 c000f124
[   51.140000] 1fa0: dec60000 c000efa0 00020000 00020000 00000003 b6e80000 00020000 000271c4
[   51.140000] 1fc0: 00020000 00020000 b6e80000 00000003 7fffe000 00000000 00000000 00020000
[   51.140000] 1fe0: 00000000 bef50b64 00013835 b6f29c76 400f0030 00000003 00000000 00000000
[   51.140000] [<c01e71a0>] (at91_pinconf_get) from [<c01e7304>] (at91_pinconf_dbg_show+0x18/0x2c0)
[   51.140000] [<c01e7304>] (at91_pinconf_dbg_show) from [<c01e6034>] (pinconf_pins_show+0xc8/0xf8)
[   51.140000] [<c01e6034>] (pinconf_pins_show) from [<c00ae0b8>] (seq_read+0x1a0/0x464)
[   51.140000] [<c00ae0b8>] (seq_read) from [<c0090dec>] (__vfs_read+0x20/0xd0)
[   51.140000] [<c0090dec>] (__vfs_read) from [<c0091508>] (vfs_read+0x7c/0x108)
[   51.140000] [<c0091508>] (vfs_read) from [<c0091d9c>] (SyS_read+0x40/0x94)
[   51.140000] [<c0091d9c>] (SyS_read) from [<c000efa0>] (ret_fast_syscall+0x0/0x3c)
[   51.140000] Code: eb010ec2 e30a0d08 e34c005a eb0ae5a7 (e5993000)
[   51.150000] ---[ end trace fb3c370da3ea4794 ]---

Fixes: a0b957f306fa ("pinctrl: at91: allow to have disabled gpio bank")
Cc: stable@vger.kernel.org # 3.18
Signed-off-by: David Dueck <davidcdueck@googlemail.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>