iio: Move __private marking before struct element priv in struct iio_dev

This is to avoid tripping up kernel-doc which filters it out before
but not after the name.

Note the formatting is less than ideal as a result so we may revisit
in future.

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

Author: jic23

include/linux/iio/iio.h

@@ -624,7 +624,7 @@ struct iio_dev {
 	const struct iio_info		*info;
 	const struct iio_buffer_setup_ops	*setup_ops;
 
-	void				*priv __private;
+	void				*__private priv;
 };
 
 int iio_device_id(struct iio_dev *indio_dev);