ACPI / hotplug: Use kobject_init_and_add() instead of _init() and _add()

Use kobject_init_and_add() since we have nothing special to do between
kobject_init() and kobject_add().

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>