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/2021/6/7/398

Signed-off-by: Christophe JAILLET <[e-mail]>
Link: https://lore.kernel.org/r/1a414c05c2[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/alteon/acenic.c

···
 	}
 	ap->name = dev->name;
 
-	if (ap->pci_using_dac)
-		dev->features |= NETIF_F_HIGHDMA;
+	dev->features |= NETIF_F_HIGHDMA;
 
 	pci_set_drvdata(pdev, 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

···
 				__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;