staging:iio:buffer scrap to_iio_buffer as it no longer has meaning.

Now buffers do not have a specific dev structure, this is garbage.
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/buffer.h

@@ -129,9 +129,6 @@ int iio_scan_mask_query(struct iio_buffer *buffer, int bit);
  **/
 int iio_scan_mask_set(struct iio_buffer *buffer, int bit);
 
-#define to_iio_buffer(d)				\
-	container_of(d, struct iio_buffer, dev)
-
 /**
  * iio_push_to_buffer() - push to a registered buffer.
  * @buffer:		IIO buffer structure for device