cxgb3: Remove useless DMA-32 fallback configuration

As stated in [1], dma_set_mask() with a 64-bit mask never fails if
dev->dma_mask is non-NULL.
So, if it fails, the 32 bits case will also fail for the same reason.

So, if dma_set_mask_and_coherent() succeeds, 'pci_using_dac' is known to be
1.

Simplify code and remove some dead code accordingly.

[1]: https://lkml.org/lkml/2021/6/7/398

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/a0e2539aefb0034091aca02c98440ea9459f1258.1641736234.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c

@@ -3204,7 +3204,7 @@ static void cxgb3_init_iscsi_mac(struct net_device *dev)
 			NETIF_F_IPV6_CSUM | NETIF_F_HIGHDMA)
 static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
-	int i, err, pci_using_dac = 0;
+	int i, err;
 	resource_size_t mmio_start, mmio_len;
 	const struct adapter_info *ai;
 	struct adapter *adapter = NULL;
@@ -3231,9 +3231,8 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto out_disable_device;
 	}
 
-	if (!dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64))) {
-		pci_using_dac = 1;
-	} else if ((err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32))) != 0) {
+	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+	if (err) {
 		dev_err(&pdev->dev, "no usable DMA configuration\n");
 		goto out_release_regions;
 	}
@@ -3309,8 +3308,8 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		netdev->features |= netdev->hw_features |
 				    NETIF_F_HW_VLAN_CTAG_TX;
 		netdev->vlan_features |= netdev->features & VLAN_FEAT;
-		if (pci_using_dac)
-			netdev->features |= NETIF_F_HIGHDMA;
+
+		netdev->features |= NETIF_F_HIGHDMA;
 
 		netdev->netdev_ops = &cxgb_netdev_ops;
 		netdev->ethtool_ops = &cxgb_ethtool_ops;