staging: iio: ad9832: convert probe to device-managed

This change does a conversion of the driver to use device-managed init
functions. The 2 regulators and the clock inits are converted to use
devm_add_action_or_reset() callbacks for de-initializing them when the
driver unloads.

And finally the devm_iio_device_register() function can be use to register
the device.

The remove hook can finally be removed and the spi_set_drvdata() call can
also be removed as the private data is no longer used.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210913115209.300665-1-aardelean@deviqon.com


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