UBIFS: do not commit twice

VFS calls '->sync_fs()' twice - first time with @wait = 0, second
time with @wait = 1. As a result, we may commit and synchronize
write-buffers twice. Avoid doing this by returning immediatelly if
@wait = 0.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -432,18 +432,19 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 	int i, err;
 	struct ubifs_info *c = sb->s_fs_info;
 	struct writeback_control wbc = {
-		.sync_mode   = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
+		.sync_mode   = WB_SYNC_ALL,
 		.range_start = 0,
 		.range_end   = LLONG_MAX,
 		.nr_to_write = LONG_MAX,
 	};
 
 	/*
-	 * Note by akpm about WB_SYNC_NONE used above: zero @wait is just an
-	 * advisory thing to help the file system shove lots of data into the
-	 * queues. If some gets missed then it'll be picked up on the second
+	 * Zero @wait is just an advisory thing to help the file system shove
+	 * lots of data into the queues, and there will be the second
 	 * '->sync_fs()' call, with non-zero @wait.
 	 */
+	if (!wait)
+		return 0;
 
 	if (sb->s_flags & MS_RDONLY)
 		return 0;