gpio-amdpt: ACPI: Use the ACPI_COMPANION() macro directly

The ACPI_HANDLE() macro is a wrapper arond the ACPI_COMPANION()
macro and the ACPI handle produced by the former comes from the
ACPI device object produced by the latter, so it is way more
straightforward to evaluate the latter directly instead of passing
the handle produced by the former to acpi_bus_get_device().

Modify pt_gpio_probe() accordingly (no intentional functional impact).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>