iio: adc: ingenic-adc: convert to IIO fwnode interface

Move from 'of_xlate()' to 'fwnode_xlate()'. The end goal is to completely
drop OF from the IIO inkernel interface.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220715122903.332535-8-nuno.sa@analog.com


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