fsl/fman: check of_get_phy_mode() return value

For unknown compatibles avoid crashing and default to SGMII.
Signed-off-by: NMadalin Bucur <madalin.bucur@nxp.com>

drivers/net/ethernet/freescale/fman/mac.c

@@ -663,6 +663,7 @@ static int mac_probe(struct platform_device *_of_dev)
 	const u8		*mac_addr;
 	u32			 val;
 	u8			fman_id;
+	int			phy_if;
 
 	dev = &_of_dev->dev;
 	mac_node = dev->of_node;
@@ -842,13 +843,14 @@ static int mac_probe(struct platform_device *_of_dev)
 	}
 
 	/* Get the PHY connection type */
-	priv->phy_if = of_get_phy_mode(mac_node);
-	if (priv->phy_if < 0) {
+	phy_if = of_get_phy_mode(mac_node);
+	if (phy_if < 0) {
 		dev_warn(dev,
-			 "of_get_phy_mode() for %s failed. Defaulting to MII\n",
+			 "of_get_phy_mode() for %s failed. Defaulting to SGMII\n",
 			 mac_node->full_name);
-		priv->phy_if = PHY_INTERFACE_MODE_MII;
+		phy_if = PHY_INTERFACE_MODE_SGMII;
 	}
+	priv->phy_if = phy_if;
 
 	priv->speed		= phy2speed[priv->phy_if];
 	priv->max_speed		= priv->speed;