thermal: sysfs: Refine the handling of trip hysteresis changes

Change trip_point_hyst_store() and replace thermal_zone_trip_updated()
with thermal_zone_set_trip_hyst() to follow the trip_point_temp_store()
code pattern for more consistency.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/5508466.Sb9uPGUboI@rjwysocki.net