dt-bindings: iio: adc: adi,ad7606: normalize textwidth

Normalize textwidth to 80 columns on the descriptions.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Guillaume Stols <gstols@baylibre.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>