Input: atmel_mxt_ts - only use first T9 instance

The driver only registers one input device, which uses the screen
parameters from the first T9 instance. The first T63 instance also uses
those parameters.

It is incorrect to send input reports from the second instances of these
objects if they are enabled: the input scaling will be wrong and the
positions will be mashed together.

This also causes problems on Android if the number of slots exceeds 32.

In the future, this could be handled by looking for enabled touch object
instances and creating an input device for each one.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Acked-by: Benson Leung <bleung@chromium.org>
Acked-by: Yufeng Shen <miletus@chromium.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>