Input: wacom - fix retrieving touch_max bug

rep_data is not an array anymore, so taking it's address when passing to
wacom_get_report() is wrong.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Tested-by: Rafi Rubin <rafi@seas.upenn.edu>
Reviewed-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>