platform/x86: huawei-wmi: do not hard-code sizes

Use `sizeof()` and `ARRAY_SIZE()` instead of
hard-coding buffer sizes and indices.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20221005150032.173198-1-pobrn@protonmail.com


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