of: check for IS_ERR()

get_phy_device() can return an ERR_PTR()

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Grant Likely <[e-mail]>

drivers/of/of_mdio.c

···
 		}
 
 		phy = get_phy_device(mdio, be32_to_cpup(addr));
-		if (!phy) {
+		if (!phy || IS_ERR(phy)) {
 			dev_err(&mdio->dev, "error probing PHY at address %i\n",
 				*addr);
 			continue;