Btrfs: do delay iput in sync_fs

We get lock inversion with umount if we allow iputs from sync_fs, so use the
delay iput flag to keep this from happening.  Thanks,
Reported-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>

fs/btrfs/super.c

@@ -862,7 +862,7 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
 		return 0;
 	}
 
-	btrfs_wait_all_ordered_extents(fs_info, 0);
+	btrfs_wait_all_ordered_extents(fs_info, 1);
 
 	trans = btrfs_attach_transaction_barrier(root);
 	if (IS_ERR(trans)) {