HID: hid-multitouch: fix input mode feature command

Zytronic panels shows a new way of setting the Input Mode feature.
This feature is put in the second usage in the HID feature, instead
of the first, as the majority of the multitouch devices.

This patch adds a detection step when the feature is presented to know
where the feature is located in the report. We can then trigger the right
command to the device. This removes the magic number "0" in the function
mt_set_input_mode.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>