This is necessary since timestamp is calculated as the last element
in iio_compute_scan_bytes().

Without this fix any userspace code reading the layout of the buffer via
sysfs will incorrectly interpret the data leading some nasty corruption.
Signed-off-by: NMarcus Folkesson <marcus.folkesson@gmail.com>
Acked-by: NLars-Peter Clausen <lars@metafoo.de>
Cc: stable@vger.kernel.org
Signed-off-by: NJonathan Cameron <jic23@kernel.org>