thermal/drivers/rcar_thermal: Constify static thermal_zone_device_ops

thermal/drivers/rcar_thermal: Constify static thermal_zone_device_ops

The only usage of rcar_thermal_zone_of_ops is to pass its address to
devm_thermal_of_zone_register(), which takes a pointer to const struct
thermal_zone_device_ops. Make it const to allow the compiler to put
it in read-only memory.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20220909182838.11154-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>