iio/axp288_adc: add missing channel info mask

Commit 65de7654 ("iio: iio: Fix iio_channel_read return if
channel havn't info") added a check for valid info masks.

This patch adds missing channel info masks for all ADC channels.
Otherwise, iio_read_channel_raw() would return -EINVAL when called
by consumer drivers.

Note that the change of _processed to _raw actually fixes an ABI abuse
in the original driver where it was used to avoid some special handling
rather than because it was correct.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>