drivers/net: Add missing unlock

Unlock the lock before leaving the function.

A simplified version of the semantic patch that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@r exists@
expression E1;
identifier f;
@@

f (...) { <+...
* spin_lock_irqsave (E1,...);
... when != E1
* return ...;
...+> }
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/sgiseeq.c

@@ -592,8 +592,10 @@ static int sgiseeq_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* Setup... */
 	len = skb->len;
 	if (len < ETH_ZLEN) {
-		if (skb_padto(skb, ETH_ZLEN))
+		if (skb_padto(skb, ETH_ZLEN)) {
+			spin_unlock_irqrestore(&sp->tx_lock, flags);
 			return NETDEV_TX_OK;
+		}
 		len = ETH_ZLEN;
 	}