saa7146: stop DMA before de-allocating DMA scatter/gather page buffers

Thanks-to: Hartmut <e9hack@googlemail.com> for pointing me the problem
and testing the fix.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/common/saa7146_video.c

@@ -1333,9 +1333,9 @@ static void buffer_release(struct videobuf_queue *q, struct videobuf_buffer *vb)
 
 	DEB_CAP(("vbuf:%p\n",vb));
 
-	release_all_pagetables(dev, buf);
-
 	saa7146_dma_free(dev,q,buf);
+
+	release_all_pagetables(dev, buf);
 }
 
 static struct videobuf_queue_ops video_qops = {