net: macb: Fix handling of fixed-link node

fixed-link nodes are treated as PHY nodes by of_mdiobus_child_is_phy().
We must check if the interface is a fixed-link before looking up for PHY
nodes.

Fixes: 7897b07 ("net: macb: convert to phylink")
Tested-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -737,6 +737,9 @@ static int macb_mdiobus_register(struct macb *bp)
 {
 	struct device_node *child, *np = bp->pdev->dev.of_node;
 
+	if (of_phy_is_fixed_link(np))
+		return mdiobus_register(bp->mii_bus);
+
 	/* Only create the PHY from the device tree if at least one PHY is
 	 * described. Otherwise scan the entire MDIO bus. We do this to support
 	 * old device tree that did not follow the best practices and did not