net: airoha: fix error branch in airoha_dev_xmit and airoha_set_gdm_ports

Fix error case management in airoha_dev_xmit routine since we need to
DMA unmap pending buffers starting from q->head.
Moreover fix a typo in error case branch in airoha_set_gdm_ports
routine.

Fixes: 23020f04 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/b628871bc8ae4861b5e2ab4db90aaf373cbb7cee.1721203880.git.lorenzo@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/airoha_eth.c

@@ -977,7 +977,7 @@ static int airoha_set_gdm_ports(struct airoha_eth *eth, bool enable)
 	return 0;
 
 error:
-	for (i--; i >= 0; i++)
+	for (i--; i >= 0; i--)
 		airoha_set_gdm_port(eth, port_list[i], false);
 
 	return err;
@@ -2431,9 +2431,11 @@ static netdev_tx_t airoha_dev_xmit(struct sk_buff *skb,
 	return NETDEV_TX_OK;
 
 error_unmap:
-	for (i--; i >= 0; i++)
-		dma_unmap_single(dev->dev.parent, q->entry[i].dma_addr,
-				 q->entry[i].dma_len, DMA_TO_DEVICE);
+	for (i--; i >= 0; i--) {
+		index = (q->head + i) % q->ndesc;
+		dma_unmap_single(dev->dev.parent, q->entry[index].dma_addr,
+				 q->entry[index].dma_len, DMA_TO_DEVICE);
+	}
 
 	spin_unlock_bh(&q->lock);
 error: