IB/mlx5: Replace ENOTSUPP usage with EOPNOTSUPP

Flow steering is supposed to return EOPNOTSUPP error
for unsupported fields and not ENOTSUPP error.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>