Btrfs: add missing blk_finish_plug in btrfs_sync_log()

commit 3da5ab56 upstream.

Add missing blk_finish_plug in btrfs_sync_log()
Signed-off-by: Forrest Liu <forrestl@synology.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/btrfs/tree-log.c

@@ -2600,6 +2600,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 	}
 
 	if (log_root_tree->log_transid_committed >= root_log_ctx.log_transid) {
+		blk_finish_plug(&plug);
 		mutex_unlock(&log_root_tree->log_mutex);
 		ret = root_log_ctx.log_ret;
 		goto out;