mtd: pxa3xx_nand: NULL dereference in pxa3xx_nand_probe

"info->cmdset" gets dereferenced in __readid() so it needs to be
initialized earlier in the function.  This bug was introduced in
18c81b18 "mtd: pxa3xx_nand: remove the flash info in driver
structure".

Cc: stable@kernel.org [2.6.37+]
Reported-and-tested-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>