thermal: intel: pch: use macro for temperature calculation

Use macro for temperature calculation

Signed-off-by: Sumeet Pawnikar <sumeet.r.pawnikar@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201210124801.13850-1-sumeet.r.pawnikar@intel.com