net: socionext: Fix a signedness bug in ave_probe()

The "phy_mode" variable is an enum and in this context GCC treats it as
an unsigned int so the error handling is never triggered.

Fixes: 4c270b55 ("net: ethernet: socionext: add AVE ethernet driver")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NKunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/socionext/sni_ave.c

@@ -1566,7 +1566,7 @@ static int ave_probe(struct platform_device *pdev)
 
 	np = dev->of_node;
 	phy_mode = of_get_phy_mode(np);
-	if (phy_mode < 0) {
+	if ((int)phy_mode < 0) {
 		dev_err(dev, "phy-mode not found\n");
 		return -EINVAL;
 	}