iio: adc: mcp320x: Simplify device removal logic

Use devm_* APIs to enable/disable regulator and to register in IIO infrastructure.

Signed-off-by: Arturas Moskvinas <arturas.moskvinas@gmail.com>
Link: https://lore.kernel.org/r/20240219074139.193464-2-arturas.moskvinas@gmail.com


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