drm/sun4i: Add missing drm_atomic_helper_shutdown at driver unbind

A call to drm_atomic_helper_shutdown is required to properly release
the internal references taken by the core and avoid warnings about
leaking objects. Add it since it was missing.

Fixes: 9026e0d1 ("drm: Add Allwinner A10 Display Engine support")
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190418132727.5128-2-paul.kocialkowski@bootlin.com

drivers/gpu/drm/sun4i/sun4i_drv.c

@@ -16,6 +16,7 @@
 #include <linux/of_reserved_mem.h>
 
 #include <drm/drmP.h>
+#include <drm/drm_atomic_helper.h>
 #include <drm/drm_fb_cma_helper.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_gem_cma_helper.h>
@@ -144,6 +145,7 @@ static void sun4i_drv_unbind(struct device *dev)
 
 	drm_dev_unregister(drm);
 	drm_kms_helper_poll_fini(drm);
+	drm_atomic_helper_shutdown(drm);
 	drm_mode_config_cleanup(drm);
 	of_reserved_mem_device_release(dev);
 	drm_dev_put(drm);