stmmac: fix phy init when attached to a phy

phy_bus_name can be NULL when "fixed-link" property isn't used.
Then, since "stmmac: do not poll phy handler when attach a switch",
phy_bus_name ptr needs to be checked before strcmp is called.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -868,6 +868,7 @@ static int stmmac_init_phy(struct net_device *dev)
 	}
 
 	/* If attached to a switch, there is no reason to poll phy handler */
+	if (priv->plat->phy_bus_name)
 		if (!strcmp(priv->plat->phy_bus_name, "fixed"))
 			phydev->irq = PHY_IGNORE_INTERRUPT;