iio: accel: kxcjk-1013: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

iio: accel: kxcjk-1013: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

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 this function.

Fixes: 0d16cd011eac ("iio: accel: kxcjk1013 3-axis accelerometer driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210501170121.512209-5-jic23@kernel.org