UBIFS: use PAGE_CACHE_MASK correctly

It has high bits set, not low bits set as the UBIFS code
assumed.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 2624411..7f1de98 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -254,7 +254,7 @@
 	}
 
 	if (!PageUptodate(page)) {
-		if (!(pos & PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)
+		if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)
 			SetPageChecked(page);
 		else {
 			err = do_readpage(page);
@@ -444,7 +444,7 @@
 
 	if (!PageUptodate(page)) {
 		/* The page is not loaded from the flash */
-		if (!(pos & PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)
+		if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)
 			/*
 			 * We change whole page so no need to load it. But we
 			 * have to set the @PG_checked flag to make the further