net/mlx5: Relax mlx5_devlink_eswitch_get() return value checking

If called from port ops, it is not needed to perform the checks in
mlx5_devlink_eswitch_get(). The reason is devlink port would not be
registered if the checks are not true. Introduce relaxed version
mlx5_devlink_eswitch_nocheck_get() and use it in port ops.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>