iio/drivers/sun4i_gpadc: Switch to new of thermal API

The thermal OF code has a new API allowing to migrate the OF
initialization to a simpler approach. The ops are no longer device
tree specific and are the generic ones provided by the core code.

Convert the ops to the thermal_zone_device_ops format and use the new
API to register the thermal zone with these generic ops.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linexp.org>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220804224349.1926752-29-daniel.lezcano@linexp.org


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>