mm/msync: use offset_in_page macro

linux/mm.h provides offset_in_page() macro.  Let's use already predefined
macro instead of (addr & ~PAGE_MASK).

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/msync.c b/mm/msync.c
index bb04d53..24e612f 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -38,7 +38,7 @@
 
 	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
 		goto out;
-	if (start & ~PAGE_MASK)
+	if (offset_in_page(start))
 		goto out;
 	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
 		goto out;