iio: light: isl29125: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

iio: light: isl29125: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

[ Upstream commit 3d4725194de6935dba2ad7c9cc075c885008f747 ]

To make code more readable, use a structure to express the channel
layout and ensure the timestamp is 8 byte aligned.

Found during an audit of all calls of uses of
iio_push_to_buffers_with_timestamp()

Fixes: 6c25539cbc46 ("iio: Add Intersil isl29125 digital color light sensor driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210501170121.512209-18-jic23@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>