Merge tag 'iio-fixes-for-3.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-linus

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.