platform/x86: wmi: use sizeof(*p) in allocation

As per the coding style guide, the preferred way
to pass the size of objects to allocator functions
is `sizeof(*p)`. Use that.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210904175450.156801-20-pobrn@protonmail.com


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