net: dsa: b53: Do not fail when IRQ are not initialized

When the Device Tree is not providing the per-port interrupts, do not fail
during b53_srab_irq_enable() but instead bail out gracefully. The SRAB driver
is used on the BCM5301X (Northstar) platforms which do not yet have the SRAB
interrupts wired up.

Fixes: 16994374a6fc ("net: dsa: b53: Make SRAB driver manage port interrupts")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/b53/b53_srab.c

@@ -415,7 +415,13 @@ static int b53_srab_irq_enable(struct b53_device *dev, int port)
 {
 	struct b53_srab_priv *priv = dev->priv;
 	struct b53_srab_port_priv *p = &priv->port_intrs[port];
-	int ret;
+	int ret = 0;
+
+	/* Interrupt is optional and was not specified, do not make
+	 * this fatal
+	 */
+	if (p->irq == -ENXIO)
+		return ret;
 
 	ret = request_threaded_irq(p->irq, b53_srab_port_isr,
 				   b53_srab_port_thread, 0,