iio: accel: hid: 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.
Note this matches what was done in all the other hid sensor drivers.
This one was missed previously due to an extra level of indirection.

Found during an audit of all calls of this function.

Fixes: a96cd0f9 ("iio: accel: hid-sensor-accel-3d: Add timestamp")
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/20210501170121.512209-4-jic23@kernel.org