hms(4): improve scroll with IICHID_SAMPLING

The current quirk is designed to discard duplicated data read from
the chip. Problem is, it also discards real events when they happen
to be identical, which is the case with scroll wheel events;
differently from X/Y they always move by fixed offset. This results
in two-finger scroll that would stop mid-way that could be fixed by
manually setting dev.hms.0.drift_thresh to 0.

To fix that, don't discard duplicates when there's wheel movement.
For users with actual duplicates problem this will result in scroll
suddenly becoming quite inertial, but it will stop moving at any touch,
so shouldn't be terrible.

PR: kern/276709
Reviewed By: wulf
Differential Revision: https://reviews.freebsd.org/D47640