sh_eth: Check for DMA mapping errors on transmit

dma_map_single() may fail if an IOMMU or swiotlb is in use, so
we need to check for this.
Signed-off-by: NBen Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -2174,6 +2174,10 @@ static int sh_eth_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 				 skb->len + 2);
 	txdesc->addr = dma_map_single(&ndev->dev, skb->data, skb->len,
 				      DMA_TO_DEVICE);
+	if (dma_mapping_error(&ndev->dev, txdesc->addr)) {
+		kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
 	txdesc->buffer_length = skb->len;
 
 	if (entry >= mdp->num_tx_ring - 1)