Input: wacom - add ABS_DISTANCE to Bamboo Pen reports

Tablet reports a distance of 0 right at highest point possible
to be in proximity and distance_max when touching tablet. Inverse
the distance since user land has no way of knowing ABS_DISTANCE
is not distance from tablet.

Signed-off-by: Chris Bagwell <chris@cnpbagwell.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>