caif: unlock on error path in cfserl_receive()

There was an spin_unlock missing on the error path.  The spin_lock was
tucked in with the declarations so it was hard to spot.  I added a new
line.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sjur Brændeland <sjurbren@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/caif/cfserl.c

@@ -59,16 +59,18 @@ static int cfserl_receive(struct cflayer *l, struct cfpkt *newpkt)
 	u8 stx = CFSERL_STX;
 	int ret;
 	u16 expectlen = 0;
+
 	caif_assert(newpkt != NULL);
 	spin_lock(&layr->sync);
 
 	if (layr->incomplete_frm != NULL) {
-
 		layr->incomplete_frm =
 		    cfpkt_append(layr->incomplete_frm, newpkt, expectlen);
 		pkt = layr->incomplete_frm;
-		if (pkt == NULL)
+		if (pkt == NULL) {
+			spin_unlock(&layr->sync);
 			return -ENOMEM;
+		}
 	} else {
 		pkt = newpkt;
 	}