[AX25/MKISS]: unbalanced spinlock_bh in ax_encaps()

The unlocking disappeared during commit
5793f4be23f0171b4999ca68a39a9157b44139f3.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/mkiss.c

@@ -524,6 +524,7 @@ static void ax_encaps(struct net_device *dev, unsigned char *icp, int len)
 	ax->dev->trans_start = jiffies;
 	ax->xleft = count - actual;
 	ax->xhead = ax->xbuff + actual;
+	spin_unlock_bh(&ax->buflock);
 }
 
 /* Encapsulate an AX.25 packet and kick it into a TTY queue. */