iio: adc: sort Makefile

The Makefile for IIO ADC drivers is intended to be sorted alphabetically.
I can be tricky to keep it sorted when adding new drivers when not all
of the existing drivers are sorted. So let's sort everything now to make
it easier to keep it sorted in the future.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20240523192412.3220547-1-dlechner@baylibre.com


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