Input: atmel_mxt_ts - print less overhead when dumping objects

Conserve limited (PAGE_SIZE) sysfs output buffer space by only showing
readable objects and not printing the object's index, which is not useful
to userspace.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>