udmabuf: constify udmabuf_ops

Reported-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180911134216.9760-5-kraxel@redhat.com

drivers/dma-buf/udmabuf.c

@@ -104,7 +104,7 @@ static void kunmap_udmabuf(struct dma_buf *buf, unsigned long page_num,
 	kunmap(vaddr);
 }
 
-static struct dma_buf_ops udmabuf_ops = {
+static const struct dma_buf_ops udmabuf_ops = {
 	.map_dma_buf	  = map_udmabuf,
 	.unmap_dma_buf	  = unmap_udmabuf,
 	.release	  = release_udmabuf,