HID: multitouch: change touch sensor detection in mt_input_configured()

To implement different methods for pen and touch, the previous
implementation has to be reworked.

This detection of the input attached to the touch sensor is the same
than the one used in mt_report().

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