generic: fix compilation warning for ar8xxx swconfig

There are 2 warning for ar8xxx swconfig.
- Fix not used dev variable when ETHERNET_PACKET_MANGLE
  is not selected
- Convert fallthrough comment to compilation macro

Signed-off-by: Ansuel Smith <[email protected]>

target/linux/generic/files/drivers/net/phy/ar8216.c

@@ -2433,7 +2433,9 @@ static int
 ar8xxx_phy_config_init(struct phy_device *phydev)
 {
 	struct ar8xxx_priv *priv = phydev->priv;
+#ifdef CONFIG_ETHERNET_PACKET_MANGLE
 	struct net_device *dev = phydev->attached_dev;
+#endif
 	int ret;
 
 	if (WARN_ON(!priv))

target/linux/generic/files/drivers/net/phy/ar8327.c

@@ -183,7 +183,7 @@ ar8327_phy_fixup(struct ar8xxx_priv *priv, int phy)
 
 	case 2:
 		ar8xxx_phy_mmd_write(priv, phy, 0x7, 0x3c, 0x0);
-		/* fallthrough */
+		fallthrough;
 	case 4:
 		ar8xxx_phy_mmd_write(priv, phy, 0x3, 0x800d, 0x803f);
 		ar8xxx_phy_dbg_write(priv, phy, 0x3d, 0x6860);