mtd: m25p80: fix null pointer dereference bug

mtd: m25p80: fix null pointer dereference bug

This patch fixes the following oops, observed with MTD_PARTITIONS=n:

m25p80 spi32766.0: m25p80 (1024 Kbytes)
Unable to handle kernel paging request for data at address 0x00000008
Faulting instruction address: 0xc03a54b0
Oops: Kernel access of bad area, sig: 11 [#1]
Modules linked in:
NIP: c03a54b0 LR: c03a5494 CTR: c01e98b8
REGS: ef82bb60 TRAP: 0300   Not tainted  (2.6.31-rc4-00167-g4733fd3)
MSR: 00029000 <EE,ME,CE>  CR: 24022022  XER: 20000000
DEAR: 00000008, ESR: 00000000
TASK = ef82c000[1] 'swapper' THREAD: ef82a000
GPR00: 00000000 ef82bc10 ef82c000 0000002e 00001eb8 ffffffff c01e9824 00000036
GPR08: c054ed40 c0542a08 00001eb8 00004000 22022022 1001a1a0 3ff8fd00 00000000
GPR16: 00000000 00000001 00000000 00000000 ef82bddc c0530000 efbef500 ef8356d0
GPR24: 00000000 ef8356d0 00000000 efbf7a00 c0530ec4 ffffffed efbf5300 c0541f98
NIP [c03a54b0] m25p_probe+0x22c/0x354
LR [c03a5494] m25p_probe+0x210/0x354
Call Trace:
[ef82bc10] [c03a5494] m25p_probe+0x210/0x354 (unreliable)
[ef82bca0] [c024e37c] spi_drv_probe+0x2c/0x3c
[ef82bcb0] [c01f1afc] driver_probe_device+0xa4/0x178
[ef82bcd0] [c01f06e8] bus_for_each_drv+0x6c/0xa8
[ef82bd00] [c01f1a34] device_attach+0x84/0xa8
...

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>