[PATCH] mm/page_alloc: use NULL instead of 0 for ptr

Use NULL instead of 0 for pointer value, eliminate sparse warnings.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>