doc: iio: ad4695: document buffered read

Update the ad4695 documentation to say that buffered reads are
supported. Since there are 4 possible modes of reading conversion data,
it is useful to know which one is actually being used, namely the
advanced sequencer mode.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20240813-iio-adc-ad4695-buffered-read-v2-2-9bb19fc1924b@baylibre.com


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