enetc: Fix a signedness bug in enetc_of_get_phy()

The "priv->if_mode" is type phy_interface_t which is an enum.  In this
context GCC will treat the enum as an unsigned int so this error
handling is never triggered.

Fixes: d4fd0404 ("enetc: Introduce basic PF and VF ENETC ethernet drivers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/enetc/enetc_pf.c

@@ -785,7 +785,7 @@ static int enetc_of_get_phy(struct enetc_ndev_priv *priv)
 	}
 
 	priv->if_mode = of_get_phy_mode(np);
-	if (priv->if_mode < 0) {
+	if ((int)priv->if_mode < 0) {
 		dev_err(priv->dev, "missing phy type\n");
 		of_node_put(priv->phy_node);
 		if (of_phy_is_fixed_link(np))