ACPI: platform: Fix file references in comment

The referenced files are named slightly different. Replace '-' with '_'
and drop the .rst ending.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>