thermal/drivers/hisi: Use round up step value

Use round up division to ensure the programmed value of threshold and the lag
are not less than what we set, and in order to keep the accuracy while using
round up division, the step value should be a rounded up value.  There is
no need to use hisi_thermal_round_temp.

Signed-off-by: Kevin Wangtao <kevin.wangtao@linaro.org>
Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org> # hikey6220
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>