net: macb: add check for dma mapping error in start_xmit()

at91ether_start_xmit() does not check for dma mapping errors.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: NAlexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb.c

@@ -2673,6 +2673,12 @@ static int at91ether_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		lp->skb_length = skb->len;
 		lp->skb_physaddr = dma_map_single(NULL, skb->data, skb->len,
 							DMA_TO_DEVICE);
+		if (dma_mapping_error(NULL, lp->skb_physaddr)) {
+			dev_kfree_skb_any(skb);
+			dev->stats.tx_dropped++;
+			netdev_err(dev, "%s: DMA mapping error\n", __func__);
+			return NETDEV_TX_OK;
+		}
 
 		/* Set address of the data in the Transmit Address register */
 		macb_writel(lp, TAR, lp->skb_physaddr);