net/mlx5e: Fix wrong error code return on FEC query failure

Advertised and configured FEC query failure resulted in printing
wrong error code.

Fixes: 6cfa9460

 ("net/mlx5e: Ethtool driver callback for query/set FEC policy")
Signed-off-by: Shay Agroskin <shayag@mellanox.com>
Reported-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>