Kobject: change drivers/acpi/system.c to use kobject_create_and_add

Stop using kobject_register for this static kobject, as it's overkill.
This way is much simpler.

Cc: Len Brown <len.brown@intel.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>