ACPI / PAD: power_saving_thread() is not freezable

power_saving_thread() calls try_to_freeze(), but the thread doesn't mark
itself freezable through set_freezable(), so the try_to_freeze()
call is useless.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>