mm/internal.h: use nth_page

Use nth_page instead of pfn_to_page(page_to_pfn
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/internal.h

@@ -247,7 +247,7 @@ static inline void mlock_migrate_page(struct page *new, struct page *old) { }
 static inline struct page *mem_map_offset(struct page *base, int offset)
 {
 	if (unlikely(offset >= MAX_ORDER_NR_PAGES))
-		return pfn_to_page(page_to_pfn(base) + offset);
+		return nth_page(base, offset);
 	return base + offset;
 }