net: macb: fix missing unlock on error in macb_start_xmit()

Fix missing unlock before return from function macb_start_xmit()
in the error handling case.

Fixes: 007e4ba3 ("net: macb: initialize checksum when using
checksum offloading")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb.c

@@ -1398,7 +1398,7 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	if (macb_clear_csum(skb)) {
 		dev_kfree_skb_any(skb);
-		return NETDEV_TX_OK;
+		goto unlock;
 	}
 
 	/* Map socket buffer for DMA transfer */