[media] s5p-mfc: set allow_zero_bytesused flag for vb2_queue_init

The s5p-mfc driver interprets a buffer with bytesused equal to 0 as a
special case indicating end-of-stream. After vb2: fix bytesused == 0
handling (8a75ffb) patch videobuf2 modified the value of bytesused if it
was 0. The allow_zero_bytesused flag was added to videobuf2 to keep
backward compatibility.

Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/platform/s5p-mfc/s5p_mfc.c

@@ -843,6 +843,13 @@ static int s5p_mfc_open(struct file *file)
 		ret = -ENOENT;
 		goto err_queue_init;
 	}
+	/* One way to indicate end-of-stream for MFC is to set the
+	 * bytesused == 0. However by default videobuf2 handles bytesused
+	 * equal to 0 as a special case and changes its value to the size
+	 * of the buffer. Set the allow_zero_bytesused flag so that videobuf2
+	 * will keep the value of bytesused intact.
+	 */
+	q->allow_zero_bytesused = 1;
 	q->mem_ops = &vb2_dma_contig_memops;
 	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY;
 	ret = vb2_queue_init(q);