dma: mv_xor: fix error checking of irq_of_parse_and_map()

The irq_of_parse_and_map() function returns 0 on failure, and does not
return an error code, so we fix the calling site of
irq_of_parse_and_map() in the mv_xor driver.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

drivers/dma/mv_xor.c

@@ -1312,8 +1312,8 @@ static int __devinit mv_xor_probe(struct platform_device *pdev)
 				dma_cap_set(DMA_INTERRUPT, cap_mask);
 
 			irq = irq_of_parse_and_map(np, 0);
-			if (irq < 0) {
-				ret = irq;
+			if (!irq) {
+				ret = -ENODEV;
 				goto err_channel_add;
 			}