Input: elantech - fix semi-mt protocol for v3 HW

commit 3c0213d17a09601e0c6c0ae0e27caf70d988290f upstream.

When the v3 hardware sees more than one finger, it uses the semi-mt
protocol to report the touches. However, it currently works when
num_fingers is 0, 1 or 2, but when it is 3 and above, it sends only 1
finger as if num_fingers was 1.

This confuses userspace which knows how to deal with extra fingers
when all the slots are used, but not when some are missing.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=90101



Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>