md-cluster: unregister thread if err happened

The two threads need to be unregistered if a node
can't join cluster successfully.
Reviewed-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/md-cluster.c

@@ -818,6 +818,8 @@ static int join(struct mddev *mddev, int nodes)
 
 	return 0;
 err:
+	md_unregister_thread(&cinfo->recovery_thread);
+	md_unregister_thread(&cinfo->recv_thread);
 	lockres_free(cinfo->message_lockres);
 	lockres_free(cinfo->token_lockres);
 	lockres_free(cinfo->ack_lockres);