hp-wmi: Fix mixing up of and/or directive

This should have been an "and". Additionally checking for !obj
is even better.

Signed-off-by: Thomas Renninger <trenn@suse.de>
CC: linux-acpi@vger.kernel.or
CC: platform-driver-x86@vger.kernel.org
CC: mjg@redhat.com
Signed-off-by: Matthew Garrett <mjg@redhat.com>