net: hisilicon: Fix signedness bug in hix5hd2_dev_probe()

The "priv->phy_mode" variable is an enum and in this context GCC will
treat it as unsigned to the error handling will never trigger.

Fixes: 57c5bc9a ("net: hisilicon: add hix5hd2 mac driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hix5hd2_gmac.c

@@ -1194,7 +1194,7 @@ static int hix5hd2_dev_probe(struct platform_device *pdev)
 		goto err_free_mdio;
 
 	priv->phy_mode = of_get_phy_mode(node);
-	if (priv->phy_mode < 0) {
+	if ((int)priv->phy_mode < 0) {
 		netdev_err(ndev, "not find phy-mode\n");
 		ret = -EINVAL;
 		goto err_mdiobus;