[9P]: Fix missing unlock before return in p9_mux_poll_start

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/9p/mux.c

@@ -222,8 +222,10 @@ static int p9_mux_poll_start(struct p9_conn *m)
 	}
 
 	if (i >= ARRAY_SIZE(p9_mux_poll_tasks)) {
-		if (vptlast == NULL)
+		if (vptlast == NULL) {
+			mutex_unlock(&p9_mux_task_lock);
 			return -ENOMEM;
+		}
 
 		P9_DPRINTK(P9_DEBUG_MUX, "put in proc %d\n", i);
 		list_add(&m->mux_list, &vptlast->mux_list);