HID: logitech-hidpp: battery: provide ONLINE property

When ONLINE isn't set, upower should ignore the battery capacity,
so there is no need to overload it with some random values.

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