HID: wacom: switch battery to devres

Simplifying the error code paths.
We need to keep wacom_destroy_battery() around for now as the wireless
module and the remotes are using it to dynamically remove the battery
supply on disconnect.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>