HID: wacom: Reset stylus buttons - Intuos4 WL

Stylus buttons have to be resetted when going out-of-prox.

Signed-off-by: Przemo Firszt <przemo@firszt.eu>
Reviewed-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>