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: 7897b071ac3b ("net: macb: convert to phylink")
Tested-by: Cristian Birsan <[e-mail]>
Signed-off-by: Codrin Ciubotariu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/cadence/macb_main.c

···
 {
 	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