drm/sun4i: Report proper vblank

The sun4i display engine doesn't have any vblank counter. Use the proper
helper for that.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

drivers/gpu/drm/sun4i/sun4i_drv.c

@@ -92,7 +92,7 @@ static struct drm_driver sun4i_drv_driver = {
 	/* Frame Buffer Operations */
 
 	/* VBlank Operations */
-	.get_vblank_counter	= drm_vblank_count,
+	.get_vblank_counter	= drm_vblank_no_hw_counter,
 	.enable_vblank		= sun4i_drv_enable_vblank,
 	.disable_vblank		= sun4i_drv_disable_vblank,
 };