thermal: intel: x86_pkg_temp_thermal: Handle invalid temperature

thermal: intel: x86_pkg_temp_thermal: Handle invalid temperature

After commit be0a3600aa1e ("thermal: sysfs: Rework the handling of trip
point updates"), THERMAL_TEMP_INVALID can be passed to sys_set_trip_temp()
and it is treated as a regular temperature value there, so the sysfs
write fails even though it is expected to succeed and disable the given
trip point.

Address this by making sys_set_trip_temp() clear its temp variable when
it is equal to THERMAL_TEMP_INVALID.

Fixes: be0a3600aa1e ("thermal: sysfs: Rework the handling of trip point updates")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/2815400.mvXUDI8C0e@rafael.j.wysocki