net: dsa: b53: per-port interrupts are optional

Make use of platform_get_irq_byname_optional() to avoid printing
messages on the kernel console that interrupts cannot be found.
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/b53/b53_srab.c

@@ -524,7 +524,7 @@ static void b53_srab_prepare_irq(struct platform_device *pdev)
 
 		port->num = i;
 		port->dev = dev;
-		port->irq = platform_get_irq_byname(pdev, name);
+		port->irq = platform_get_irq_byname_optional(pdev, name);
 		kfree(name);
 	}