tehuti: Use dma_set_mask_and_coherent() and simplify code

Use dma_set_mask_and_coherent() instead of unrolling it with some
dma_set_mask()+dma_set_coherent_mask().

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

That said, 'pci_using_dac' can only be 1 after a successful
dma_set_mask_and_coherent().

Simplify code and remove some dead code accordingly.

[1]: https://lkml.org/lkml/2021/6/7/398
Signed-off-by: Christophe JAILLET <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/tehuti/tehuti.c

···
 {
 	struct net_device *ndev;
 	struct bdx_priv *priv;
-	int err, pci_using_dac, port;
 	unsigned long pciaddr;
 	u32 regionSize;
 	struct pci_nic *nic;
+	int err, port;
 
 	ENTER;
 
···
 	if (err)			/* it triggers interrupt, dunno why. */
 		goto err_pci;		/* it's not a problem though */
 
-	if (!(err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64))) &&
-	    !(err = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64)))) {
-		pci_using_dac = 1;
-	} else {
-		if ((err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32))) ||
-		    (err = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32)))) {
-			pr_err("No usable DMA configuration, aborting\n");
-			goto err_dma;
-		}
-		pci_using_dac = 0;
+	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+	if (err) {
+		pr_err("No usable DMA configuration, aborting\n");
+		goto err_dma;
 	}
 
 	err = pci_request_regions(pdev, BDX_DRV_NAME);
···
 		/* these fields are used for info purposes only
 		 * so we can have them same for all ports of the board */
 		ndev->if_port = port;
-		ndev->features = NETIF_F_IP_CSUM | NETIF_F_SG | NETIF_F_TSO
-		    | NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_CTAG_RX |
-		    NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_RXCSUM
-		    ;
+		ndev->features = NETIF_F_IP_CSUM | NETIF_F_SG | NETIF_F_TSO |
+		    NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_CTAG_RX |
+		    NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_RXCSUM |
+		    NETIF_F_HIGHDMA;
+
 		ndev->hw_features = NETIF_F_IP_CSUM | NETIF_F_SG |
 			NETIF_F_TSO | NETIF_F_HW_VLAN_CTAG_TX;
-
-		if (pci_using_dac)
-			ndev->features |= NETIF_F_HIGHDMA;
 
 	/************** priv ****************/
 		priv = nic->priv[port] = netdev_priv(ndev);