netiucv: 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: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
index 1ba4509..be716e4 100644
--- a/drivers/s390/net/netiucv.c
+++ b/drivers/s390/net/netiucv.c
@@ -1312,7 +1312,7 @@
 
 	if (netiucv_test_and_set_busy(dev)) {
 		IUCV_DBF_TEXT(data, 2, "EBUSY from netiucv_tx\n");
-		return -EBUSY;
+		return NETDEV_TX_BUSY;
 	}
 	dev->trans_start = jiffies;
 	rc = netiucv_transmit_skb(privptr->conn, skb) != 0;