[ASUS_ACPI] work around Samsung P30s oops

The code used to rely on a certain method to return a NULL buffer, which
is now hardly possible with the implicit return code on by default. This
sort of fixes bugs #5067 and #5092 for now.

Note: this patch makes the driver unusable on said machines (and on said
machines only) iff acpi=strict is specified, but it seems noone really uses
that.

Signed-off-by: Karol Kozimor <sziwan@hell.org.pl>
Signed-off-by: Len Brown <len.brown@intel.com>