UBIFS: do not use WB_SYNC_HOLD

WB_SYNC_HOLD is going to be zapped so we should not use it. Use
%WB_SYNC_NONE instead. Here is what akpm said:

"I think I'll just switch that to WB_SYNC_NONE.  The `wait==0' mode is
just an advisory thing to help the fs shove lots of data into the
queues.  If some gets missed then it'll be picked up on the second
->sync_fs call, with wait==1."

Thanks to Randy Dunlap for catching this.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ubifs/super.c

@@ -432,12 +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_HOLD,
+		.sync_mode   = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
 		.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
+	 * '->sync_fs()' call, with non-zero @wait.
+	 */
+
 	if (sb->s_flags & MS_RDONLY)
 		return 0;