gpio: mvebu: avoid error message for optional IRQ

platform_get_irq() will generate an error message if the requested irq
is not present

  mvebu-gpio f1010140.gpio: IRQ index 3 not found

use platform_get_irq_optional() to avoid the error message being
generated.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-mvebu.c

@@ -1247,7 +1247,7 @@ static int mvebu_gpio_probe(struct platform_device *pdev)
 	 * pins.
 	 */
 	for (i = 0; i < 4; i++) {
-		int irq = platform_get_irq(pdev, i);
+		int irq = platform_get_irq_optional(pdev, i);
 
 		if (irq < 0)
 			continue;