mtd: denali_dt: Change return value to fix smatch warning

platform_get_irq() also returns -ENXIO upon failure.
Use it instead of hardcoded return type.

Fixes the following smatch warning:
drivers/mtd/nand/denali_dt.c:93 denali_dt_probe() info:
why not propagate 'denali->irq' from platform_get_irq() instead of (-6)?
Signed-off-by: NSachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/denali_dt.c

@@ -90,7 +90,7 @@ static int denali_dt_probe(struct platform_device *ofdev)
 	denali->irq = platform_get_irq(ofdev, 0);
 	if (denali->irq < 0) {
 		dev_err(&ofdev->dev, "no irq defined\n");
-		return -ENXIO;
+		return denali->irq;
 	}
 
 	denali->flash_reg = request_and_map(&ofdev->dev, denali_reg);