rocker: 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.

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/9ba2d13099d216f3df83e50ad33a05504c90fe7c.1641744274.git.christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/rocker/rocker_main.c

@@ -2870,20 +2870,11 @@ static int rocker_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		goto err_pci_request_regions;
 	}
 
-	err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
-	if (!err) {
-		err = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64));
-		if (err) {
-			dev_err(&pdev->dev, "dma_set_coherent_mask failed\n");
-			goto err_pci_set_dma_mask;
-		}
-	} else {
-		err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32));
+	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
 	if (err) {
 		dev_err(&pdev->dev, "dma_set_mask failed\n");
 		goto err_pci_set_dma_mask;
 	}
-	}
 
 	if (pci_resource_len(pdev, 0) < ROCKER_PCI_BAR0_SIZE) {
 		dev_err(&pdev->dev, "invalid PCI region size\n");