thermal/drivers/rcar_gen3_thermal: Fix coefficient calculations

The fixed value of 157 used in the calculations are only correct for
M3-W, on other Gen3 SoC it should be 167. The constant can be derived
correctly from the static TJ_3 constant and the SoC specific TJ_1 value.
Update the calculation be correct on all Gen3 SoCs.

Fixes: 4eb39f79

 ("thermal: rcar_gen3_thermal: Update value of Tj_1")
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210605085211.564909-1-niklas.soderlund+renesas@ragnatech.se