net: stmmac: Fixed link does not need MDIO Bus

When using fixed link we don't need the MDIO bus support.
Reported-by: Heiko Stuebner <heiko@sntech.de>
Reported-by: kernelci.org bot <bot@kernelci.org>
Fixes: d3e014ec ("net: stmmac: platform: Fix MDIO init for platforms without PHY")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Acked-by: Sriram Dash <Sriram.dash@samsung.com>
Tested-by: Patrice Chotard <patrice.chotard@st.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail> # Lamobo R1 (fixed-link + MDIO sub node for roboswitch).
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -320,7 +320,7 @@ static int stmmac_mtl_setup(struct platform_device *pdev,
 static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
 			 struct device_node *np, struct device *dev)
 {
-	bool mdio = false;
+	bool mdio = !of_phy_is_fixed_link(np);
 	static const struct of_device_id need_mdio_ids[] = {
 		{ .compatible = "snps,dwc-qos-ethernet-4.10" },
 		{},