Replace adc-scan.sh script with iio_readdev

We should discover whether or not we can replace the /bin/adc-scan.sh script with something that already exists -- [iio_readdev](https://manpages.debian.org/testing/libiio-utils/iio_readdev.1.en.html).  The less bespoke scripting we need to maintain, the better (generally)

Issue originally raised [here](https://github.com/uniclogs/uniclogs-linux/pull/17#discussion_r2835129686).
