Input: atmel_mxt_ts - define helper functions for size and instances

These two object table entry fields are reported 1 less than their value.
When used, however, we always want the actual size and instances.

To keep the object size and instances 1-byte fields, and thus preserve
the object-table struct's 6-byte packed alignment, add some convenient
accessor functions that do the +1 every time these fields are accessed.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
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>