net: alx: remove redundant variable old_duplex

Variable old_duplex is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
warning: variable 'old_duplex' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/alx/main.c

@@ -1279,7 +1279,6 @@ static void alx_check_link(struct alx_priv *alx)
 	struct alx_hw *hw = &alx->hw;
 	unsigned long flags;
 	int old_speed;
-	u8 old_duplex;
 	int err;
 
 	/* clear PHY internal interrupt status, otherwise the main
@@ -1288,7 +1287,6 @@ static void alx_check_link(struct alx_priv *alx)
 	alx_clear_phy_intr(hw);
 
 	old_speed = hw->link_speed;
-	old_duplex = hw->duplex;
 	err = alx_read_phy_link(hw);
 	if (err < 0)
 		goto reset;