thermal/drivers/rcar_gen3_thermal: Store TSC id as unsigned int

The TSC id and number of TSC ids should be stored as unsigned int as
they can't be negative. Fix the datatype of the loop counter 'i' and
rcar_gen3_thermal_tsc.id to reflect this.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210804091818.2196806-3-niklas.soderlund+renesas@ragnatech.se