net/mlx5e: Use mlx5e_rqt_get_rqtn to access RQT hardware id

In order to abstract from implementation details of mlx5e_rqt, use the
mlx5e_rqt_get_rqtn getter instead of accessing the field directly.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>