iio: adc: rockchip_saradc: move all of probe to devm-functions

Parts of the saradc probe rely on devm functions and later parts do not.
This makes it more difficult to for example enable triggers via their
devm-functions and would need more undo-work in remove.

So to make life easier for the driver, move the rest of probe calls
also to their devm-equivalents.

This includes moving the clk- and regulator-disabling to a devm_action
so that they gets disabled both during remove and in the error case
in probe, after the action is registered.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>