HID: magicmouse: avoid setting up battery timer when not needed

Currently, the battery timer is set up for all devices using
hid-magicmouse, irrespective of whether they actually need it or not.

The current implementation requires the battery timer for Magic Mouse 2
and Magic Trackpad 2 when connected via USB only. Add checks to ensure
that the battery timer is only set up when they are connected via USB.

Fixes: 0b91b4e4 ("HID: magicmouse: Report battery level over USB")
Cc: stable@vger.kernel.org
Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>