Btrfs: add missing blk_finish_plug in btrfs_sync_log()

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>

fs/btrfs/tree-log.c

@@ -2591,6 +2591,7 @@ 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;