greth: fall through to common return statement on error

There doesn't seem to be any reason to explicitly return
NETDEV_TX_OK as err is set to NETDEV_TX_OK in all cases that
reach this point.
Signed-off-by: NSimon Horman <horms@verge.net.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/greth.c

@@ -560,8 +560,6 @@ greth_start_xmit_gbit(struct sk_buff *skb, struct net_device *dev)
 	if (net_ratelimit())
 		dev_warn(greth->dev, "Could not create TX DMA mapping\n");
 	dev_kfree_skb(skb);
-	return NETDEV_TX_OK;
-
 out:
 	return err;
 }