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>

drivers/iio/kfifo_buf.c

@@ -95,7 +95,7 @@ static int iio_set_length_kfifo(struct iio_buffer *r, int length)
 }
 
 static int iio_store_to_kfifo(struct iio_buffer *r,
-			      u8 *data)
+			      const void *data)
 {
 	int ret;
 	struct iio_kfifo *kf = iio_to_kfifo(r);