Every rcar_thermal_update_temp() return value will be checked.

And also, rcar_thermal_get_temp() always call
rcar_thermal_update_temp() by this patch.
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: NEduardo Valentin <edubezval@gmail.com>