thermal/drivers/hisi: Move the clk setup in the corresponding functions

The sensor's clock is enabled and disabled outside of the probe and
disable function. Moving the corresponding action in the
hisi_thermal_setup() and hisi_thermal_disable_sensor(), factors out
some lines of code and makes the code more symmetric.

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>