net: nixge: Fix a signedness bug in nixge_probe()

The "priv->phy_mode" is an enum and in this context GCC will treat it
as an unsigned int so it can never be less than zero.

Fixes: 492caffa ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/ni/nixge.c

@@ -1347,7 +1347,7 @@ static int nixge_probe(struct platform_device *pdev)
 	}
 
 	priv->phy_mode = of_get_phy_mode(pdev->dev.of_node);
-	if (priv->phy_mode < 0) {
+	if ((int)priv->phy_mode < 0) {
 		netdev_err(ndev, "not find \"phy-mode\" property\n");
 		err = -EINVAL;
 		goto unregister_mdio;