net/mlx4: Address build warnings on set but not used variables

Handle the compiler warnings on variables which are set but not used
by removing the relevant variable or casting a return value which is
ignored on purpose to void.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/mellanox/mlx4/port.c b/drivers/net/ethernet/mellanox/mlx4/port.c
index 55b12e6..1fe2c7a 100644
--- a/drivers/net/ethernet/mellanox/mlx4/port.c
+++ b/drivers/net/ethernet/mellanox/mlx4/port.c
@@ -338,13 +338,12 @@
 void mlx4_unregister_mac(struct mlx4_dev *dev, u8 port, u64 mac)
 {
 	u64 out_param;
-	int err;
 
 	if (mlx4_is_mfunc(dev)) {
 		set_param_l(&out_param, port);
-		err = mlx4_cmd_imm(dev, mac, &out_param, RES_MAC,
-				   RES_OP_RESERVE_AND_MAP, MLX4_CMD_FREE_RES,
-				   MLX4_CMD_TIME_CLASS_A, MLX4_CMD_WRAPPED);
+		(void) mlx4_cmd_imm(dev, mac, &out_param, RES_MAC,
+				    RES_OP_RESERVE_AND_MAP, MLX4_CMD_FREE_RES,
+				    MLX4_CMD_TIME_CLASS_A, MLX4_CMD_WRAPPED);
 		return;
 	}
 	__mlx4_unregister_mac(dev, port, mac);