thermal: netlink: Pass pointers to thermal_notify_tz_trip_change()

Instead of requiring the caller of thermal_notify_tz_trip_change() to
provide specific values needed to populate struct param in it, make it
extract those values from objects passed to it by the caller via const
pointers.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>