iio: light: adjd_s311: move buffer on adjd_s311_data object

iio: light: adjd_s311: move buffer on adjd_s311_data object

This change moves the entire buffer on the private adjd_s311_data type.
Since the device has 4 channels, it's not a big waste to just allocate the
maximum possible buffer and use only what's needed.

This is in contrast with free-ing and re-allocating the buffer on the
update_scan_mode hook.

Since the driver pushes buffer data with
iio_push_to_buffers_with_timestamp(), the buffer must also include a
64-bit buffer for the timestamp, for each sample-set.

With this change, the adjd_s311_update_scan_mode() is no longer needed.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210705071456.649659-1-aardelean@deviqon.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>