net: atlantic: fix potential error handling

Code inspection found that in case of mapping error we do return current
'ret' value. But beside error, it is used to count number of descriptors
allocated for the packet. In that case map_skb function could return '1'.

Changing it to return zero (number of mapped descriptors for skb)

Fixes: 018423e9 ("net: ethernet: aquantia: Add ring support code")
Signed-off-by: Pavel Belous <pbelous@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Dmitry Bogdanov <dbogdanov@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aquantia/atlantic/aq_nic.c

@@ -533,8 +533,10 @@ unsigned int aq_nic_map_skb(struct aq_nic_s *self, struct sk_buff *skb,
 				     dx_buff->len,
 				     DMA_TO_DEVICE);
 
-	if (unlikely(dma_mapping_error(aq_nic_get_dev(self), dx_buff->pa)))
+	if (unlikely(dma_mapping_error(aq_nic_get_dev(self), dx_buff->pa))) {
+		ret = 0;
 		goto exit;
+	}
 
 	first = dx_buff;
 	dx_buff->len_pkt = skb->len;