iio: amplifiers: ad8366: refactor device resource management

iio: amplifiers: ad8366: refactor device resource management

Adhere modern device resource management with the following:
- Voltage regulator managed and enabled internally;
- IIO device registration handled with devm_iio_device_register();
- removal of goto's from the probe function;
- ad8366_remove() removed as it is not needed anymore;

With the drop of goto's dev_err_probe() is used to report probe errors.

Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>