HID: logitech-hidpp: make sure we only register one battery per device

Simple check to add, huge improvement :)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>