thermal: core: Do not call handle_thermal_trip() if zone temperature is invalid

Make __thermal_zone_device_update() bail out if update_temperature()
fails to update the zone temperature because __thermal_zone_get_temp()
has returned an error and the current zone temperature is
THERMAL_TEMP_INVALID (user space receiving netlink thermal messages,
thermal debug code and thermal governors may get confused otherwise).

Fixes: 9ad18043 ("thermal: core: Send trip crossing notifications at init time if needed")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>