net/mlx5: Fix err prints and return when creating termination table

Fix print to print correct error code and not using IS_ERR() which
will just result in always printing 1.
Also return real err instead of always -EOPNOTSUPP.

Fixes: 10caabda ("net/mlx5e: Use termination table for VLAN push actions")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>