ctcm: invalid return code from hard_start_xmit

Avoid kernel warning by using the correct hard_start_xmit return
code NETDEV_TX_BUSY for skb requeuing.
Signed-off-by: NUrsula Braun <ursula.braun@de.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/s390/net/ctcm_main.c

@@ -906,11 +906,11 @@ static int ctcm_tx(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	if (ctcm_test_and_set_busy(dev))
-		return -EBUSY;
+		return NETDEV_TX_BUSY;
 
 	dev->trans_start = jiffies;
 	if (ctcm_transmit_skb(priv->channel[WRITE], skb) != 0)
-		return 1;
+		return NETDEV_TX_BUSY;
 	return 0;
 }