iio: dmaengine-buffer: Use sysfs_emit()

sysfs_emit() is preferred over raw s*printf() for sysfs attributes since it
knows about the sysfs buffer specifics and has some built-in checks for
size and alignment.

Use sysfs_emit() for the `length_align_bytes` buffer attribute.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211216185217.1054495-3-lars@metafoo.de


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>