net: alteon: Simplify DMA setting

As stated in [1], dma_set_mask() 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.

If dma_set_mask_and_coherent() succeeds, 'ap->pci_using_dac' is known to be
1. So 'pci_using_dac' can be removed from the 'struct ace_private'.

Simplify code and remove some dead code accordingly.

[1]: https://lkml.org/lkml/2021/6/7/398Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/1a414c05c27b21c661aef61dffe1adcd1578b1f5.1641651917.git.christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/alteon/acenic.c

@@ -589,8 +589,7 @@ static int acenic_probe_one(struct pci_dev *pdev,
 	}
 	ap->name = dev->name;
 
-	if (ap->pci_using_dac)
-		dev->features |= NETIF_F_HIGHDMA;
+	dev->features |= NETIF_F_HIGHDMA;
 
 	pci_set_drvdata(pdev, dev);
 
@@ -1130,11 +1129,7 @@ static int ace_init(struct net_device *dev)
 	/*
 	 * Configure DMA attributes.
 	 */
-	if (!dma_set_mask(&pdev->dev, DMA_BIT_MASK(64))) {
-		ap->pci_using_dac = 1;
-	} else if (!dma_set_mask(&pdev->dev, DMA_BIT_MASK(32))) {
-		ap->pci_using_dac = 0;
-	} else {
+	if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(64))) {
 		ecode = -ENODEV;
 		goto init_error;
 	}

drivers/net/ethernet/alteon/acenic.h

@@ -692,7 +692,6 @@ struct ace_private
 				__attribute__ ((aligned (SMP_CACHE_BYTES)));
 	u32			last_tx, last_std_rx, last_mini_rx;
 #endif
-	int			pci_using_dac;
 	u8			firmware_major;
 	u8			firmware_minor;
 	u8			firmware_fix;