Jonathan writes:
First round of IIO fixes for the 3.19 cycle.
* ad799x fix ad7991/ad7995/ad7999 setup as they do not have a configuration
register to write to. It is written during the convesion sequence. As
such we don't want to write to it at other times.
* Fix iio_channel_read utility function to return to ensure it is apparent
if the relevant element is not there. This avoids using a wrong value
if some channels have the element and others do not.
8ecb55b849