net: dsa: lantiq_gswip: ignore MDIO buses disabled in OF

If the "lantiq,xrx200-mdio" child has status = "disabled", the MDIO bus
creation should be avoided. Use of_device_is_available() to check for
that, and take advantage of 2 facts:

- of_device_is_available(NULL) returns false
- of_node_put(NULL) is a no-op

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/lantiq_gswip.c

@@ -510,11 +510,11 @@ static int gswip_mdio(struct gswip_priv *priv)
 	struct device_node *mdio_np, *switch_np = priv->dev->of_node;
 	struct device *dev = priv->dev;
 	struct mii_bus *bus;
-	int err;
+	int err = 0;
 
 	mdio_np = of_get_compatible_child(switch_np, "lantiq,xrx200-mdio");
-	if (!mdio_np)
-		return 0;
+	if (!of_device_is_available(mdio_np))
+		goto out_put_node;
 
 	bus = devm_mdiobus_alloc(dev);
 	if (!bus) {