iio: adc: ad7476: implement devm_add_action_or_reset

Use devm_add_action_or_reset to automatically disable the device
when it is removed or an error occurs during probe routine.

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>