ACPI / scan: Fix acpi_bus_id_list bookkeeping

acpi_device_add() allocates and adds an element to acpi_bus_id_list
(or increments the instance count if the device's HID is already
present in the list), but the element is never deleted from the list
nor freed. Fix it.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>