net: bcmgenet: Fix NULL vs IS_ERR() checking

The phy_attach() function does not return NULL. It returns error pointers.

Signed-off-by: Miaoqian Lin <[e-mail]>
Acked-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/broadcom/genet/bcmmii.c

···
 		 * Internal or external PHY with MDIO access
 		 */
 		phydev = phy_attach(priv->dev, phy_name, pd->phy_interface);
-		if (!phydev) {
+		if (IS_ERR(phydev)) {
 			dev_err(kdev, "failed to register PHY device\n");
-			return -ENODEV;
+			return PTR_ERR(phydev);
 		}
 	} else {
 		/*