iio: iio_push_to_buffers(): Change type of 'data' to const void *

Change the type of the 'data' parameter for iio_push_to_buffers() from 'u8 *' to
'const void *'. Drivers typically use the correct type (e.g. __be16 *) for their
data buffer. When passing the buffer to iio_push_to_buffers() it needs to be
cast to 'u8 *' for the compiler to not complain (and also having to add __force
if we want to keep sparse happy as well). Since the buffer implementation should
not care about the data layout (except the size of one sample) using a void
pointer is the correct thing to do. Also make it const as the buffer
implementations are not supposed to modify it.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
index 2bac0eb..e5507e9 100644
--- a/include/linux/iio/buffer.h
+++ b/include/linux/iio/buffer.h
@@ -36,7 +36,7 @@
  * any of them not existing.
  **/
 struct iio_buffer_access_funcs {
-	int (*store_to)(struct iio_buffer *buffer, u8 *data);
+	int (*store_to)(struct iio_buffer *buffer, const void *data);
 	int (*read_first_n)(struct iio_buffer *buffer,
 			    size_t n,
 			    char __user *buf);
@@ -81,7 +81,7 @@
 	bool					stufftoread;
 	const struct attribute_group *attrs;
 	struct list_head			demux_list;
-	unsigned char				*demux_bounce;
+	void					*demux_bounce;
 	struct list_head			buffer_list;
 };
 
@@ -120,7 +120,7 @@
  * @indio_dev:		iio_dev structure for device.
  * @data:		Full scan.
  */
-int iio_push_to_buffers(struct iio_dev *indio_dev, unsigned char *data);
+int iio_push_to_buffers(struct iio_dev *indio_dev, const void *data);
 
 int iio_update_demux(struct iio_dev *indio_dev);