mm/page_isolation.c: fix the function comments

Commit fea85cff ("mm/page_isolation.c: return last tested pfn rather
than failure indicator") changed the meaning of the return value.  Let's
change the function comments as well.
Signed-off-by: NNeil Zhang <neilzhang1123@hotmail.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/page_isolation.c

@@ -215,7 +215,7 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
  * all pages in [start_pfn...end_pfn) must be in the same zone.
  * zone->lock must be held before call this.
  *
- * Returns 1 if all pages in the range are isolated.
+ * Returns the last tested pfn.
  */
 static unsigned long
 __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,