iio: buffer: fix coding style warnings

Just cosmetics. No functional change intended...
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20230216101452.591805-4-nuno.sa@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>