iio: light: as73211: fix channel handling in only-color triggered buffer

The channel index is off by one unit if AS73211_SCAN_MASK_ALL is not
set (optimized path for color channel readings), and it must be shifted
instead of leaving an empty channel for the temperature when it is off.

Once the channel index is fixed, the uninitialized channel must be set
to zero to avoid pushing uninitialized data.

Add available_scan_masks for all channels and only-color channels to let
the IIO core demux and repack the enabled channels.

Cc: stable@vger.kernel.org
Fixes: 403e5586 ("iio: light: as73211: New driver")
Tested-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241214-iio_memset_scan_holes-v4-1-260b395b8ed5@gmail.com


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