thermal/drivers/hisi: Remove thermal data back pointer

The presence of the thermal data pointer in the sensor structure has the unique
purpose of accessing the thermal data in the interrupt handler.

The sensor pointer is passed when registering the interrupt handler, replace the
cookie by the thermal data pointer, so the back pointer is no longer needed.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>