HID: multitouch: Fix fields from pen report ID being interpreted for multitouch

Fields like HID_DG_CONTACTCOUNT are outside of the physical collection,
but within the application collection and report ID.  Make sure to catch
those fields that are not part of the mt_report_id and return 0 so they
can be processed with the pen.  Otherwise, the wrong HID_DG_CONTACTCOUNT
will be applied to cc_index and result in dereferencing a null pointer in
mt_touch_report.

Signed-off-by: Brent Adam <brentadam@smarttech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>