Input: wacom - clean up wacom_query_tablet_data

Rewrites this function to be easier to read and understand. The new
function 'wacom_set_device_mode' now handles the grunt work of
assembling the proper feature report, sending it to the device,
and ensuring the setting "sticks".

Signed-off-by: Jason Gerecke <killertofu@gmail.com>
Tested-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>