net: stmmac: fix invalid call to mdiobus_get_phy()

In a number of cases the driver assigns a default value of -1 to
priv->plat->phy_addr. This may result in calling mdiobus_get_phy()
with addr parameter being -1. Therefore check for this scenario and
bail out before calling mdiobus_get_phy().

Fixes: 42e8702 ("net: stmmac: Fix case when PHY handle is not present")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/669f9671-ecd1-a41b-2727-7b73e3003985@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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

@@ -1150,6 +1150,11 @@ static int stmmac_init_phy(struct net_device *dev)
 		int addr = priv->plat->phy_addr;
 		struct phy_device *phydev;
 
+		if (addr < 0) {
+			netdev_err(priv->dev, "no phy found\n");
+			return -ENODEV;
+		}
+
 		phydev = mdiobus_get_phy(priv->mii, addr);
 		if (!phydev) {
 			netdev_err(priv->dev, "no phy at addr %d\n", addr);