With CONFIG_SPARSEMEM=y:

mm/rmap.c:579: warning: format '%lx' expects type 'long unsigned int', but argument 2 has type 'int'

Make __page_to_pfn() return unsigned long.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>