usb: host: xhci-plat: 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://lore.kernel.org/linux-kernel/YL3vSPK5DXTNvgdx@infradead.org/#tSigned-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/178f859197bebb385609a7c9458fb972ed312e5d.1642233968.git.christophe.jaillet@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-plat.c

@@ -226,20 +226,13 @@ static int xhci_plat_probe(struct platform_device *pdev)
 	if (!sysdev)
 		sysdev = &pdev->dev;
 
-	/* Try to set 64-bit DMA first */
 	if (WARN_ON(!sysdev->dma_mask))
 		/* Platform did not initialize dma_mask */
-		ret = dma_coerce_mask_and_coherent(sysdev,
-						   DMA_BIT_MASK(64));
+		ret = dma_coerce_mask_and_coherent(sysdev, DMA_BIT_MASK(64));
 	else
 		ret = dma_set_mask_and_coherent(sysdev, DMA_BIT_MASK(64));
-
-	/* If seting 64-bit DMA mask fails, fall back to 32-bit DMA mask */
-	if (ret) {
-		ret = dma_set_mask_and_coherent(sysdev, DMA_BIT_MASK(32));
-		if (ret)
-			return ret;
-	}
+	if (ret)
+		return ret;
 
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);