net/mlx5e: Use helper API to get devlink port index for all port flavours

Use existing helper API to get unique devlink port index for all
devlink port flavours.

Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>