iio: adc: hx711: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

iio: adc: hx711: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

[ Upstream commit afe2a789fbf7acd1a05407fc7839cc08d23825e3 ]

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: b54522b00231 ("iio: hx711: add triggered buffer support")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Andreas Klinger <ak@it-klinger.de>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210613152301.571002-3-jic23@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>