mlxsw: Remove unused mlxsw_core_port_type_get()

Function mlxsw_core_port_type_get() is no longer used. So remove it.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>