platform/x86: wmi: introduce helper to retrieve event data

Previously, `acpi_wmi_notify_handler()` and `wmi_get_event_data()`
shared more or less the exact same code to query the data for
a particular event.

Introduce a function to get rid of the duplication, and use it
from `acpi_wmi_notify_handler()` and `wmi_get_event_data()`.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210904175450.156801-30-pobrn@protonmail.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>