NET: ksz884x, fix lock imbalance

Stanse found that one error path (when alloc_skb fails) in netdev_tx
omits to unlock hw_priv->hwlock. Fix that.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tristram Ha <Tristram.Ha@micrel.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>