iio: chemical: atlas: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

Variable location for the timestamp, so just use __aligned(8)
to ensure it is always possible to naturally align it.

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

Fixes tag is not accurate, but it will need manual backporting beyond
that point if anyone cares.

Fixes: 0d15190f ("iio: chemical: atlas-ph-sensor: rename atlas-ph-sensor to atlas-sensor")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Link: https://lore.kernel.org/r/20210501171352.512953-6-jic23@kernel.org