[MTD] [NOR] Use NULL instead of 0 for pointer to shut sparse up.

Use NULL instead of 0 for pointer:
drivers/mtd/chips/cfi_cmdset_0001.c:2258:43: warning: Using plain integer as NULL pointer

Other changes by inspection.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>