thermal: rcar_thermal: don't call thermal_zone_device_unregister when USE_OF_THERMAL

devm_thermal_zone_of_sensor_register() case doesn't need to call
thermal_zone_device_unregister().
Otherwise, rcar-thermal can't register thermal zone again after rebind.
This patch fixes it.

Signed-off-by: Bui Duc Phuc <bd-phuc@jinso.co.jp>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>