DMA-API: dma: dw_dmac.c: convert to use dma_coerce_mask_and_coherent()

This code sequence:
	if (!pdev->dev.dma_mask) {
		pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
		pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
	}
bypasses the architectures check on the DMA mask.  It can be replaced
with dma_coerce_mask_and_coherent(), avoiding the direct initialization
of this mask.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/dma/dw/platform.c

@@ -191,11 +191,9 @@ static int dw_probe(struct platform_device *pdev)
 	if (IS_ERR(chip->regs))
 		return PTR_ERR(chip->regs);
 
-	/* Apply default dma_mask if needed */
-	if (!dev->dma_mask) {
-		dev->dma_mask = &dev->coherent_dma_mask;
-		dev->coherent_dma_mask = DMA_BIT_MASK(32);
-	}
+	err = dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
+	if (err)
+		return err;
 
 	pdata = dev_get_platdata(dev);
 	if (!pdata)