acer-wmi: support integer return type from WMI methods

Acer WMID_GUID1/2 method's return value was declared to integer
type on Gateway notebook.
So, add this patch for support integer return type.

Reference: bko#33032
	https://bugzilla.kernel.org/show_bug.cgi?id=33032



Tested on Gateway NV5909H laptop

Tested-by: Filipus Klutiero <chealer@gmail.com>
Cc: Carlos Corbacho <carlos@strangeworlds.co.uk>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Thomas Renninger <trenn@suse.de>
Signed-off-by: Lee, Chun-Yi <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>