iio: dac: ad5770r: use devm_regulator_get_enable_read_voltage()

Simplify the code by using devm_regulator_get_enable_read_voltage().

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241023-iio-regulator-refactor-round-5-v1-11-d0bd396b3f50@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>