et131x: 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.

Moreover, dma_set_mask_and_coherent() returns 0 or -EIO, so the return
code of the function can be used directly. There is no need to 'rc = -EIO'
explicitly.

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/b9aa46e7e5a5aa61f56aac5ea439930f41ad9946.1641726804.git.christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/agere/et131x.c

@@ -3914,10 +3914,9 @@ static int et131x_pci_setup(struct pci_dev *pdev,
 	pci_set_master(pdev);
 
 	/* Check the DMA addressing support of this device */
-	if (dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64)) &&
-	    dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32))) {
+	rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+	if (rc) {
 		dev_err(&pdev->dev, "No usable DMA addressing method\n");
-		rc = -EIO;
 		goto err_release_res;
 	}