drm/zte: Use drm_atomic_helper_shutdown

drm_plane_helper_disable is a non-atomic drivers only function, and
will blow up (since no one passes the locking context it needs).

Atomic drivers which want to quiescent their hw on unload should
use drm_atomic_helper_shutdown() instead.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Shawn Guo <shawnguo@kernel.org>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20181004202446.22905-15-daniel.vetter@ffwll.ch

drivers/gpu/drm/zte/zx_plane.c

@@ -446,7 +446,6 @@ static const struct drm_plane_helper_funcs zx_gl_plane_helper_funcs = {
 
 static void zx_plane_destroy(struct drm_plane *plane)
 {
-	drm_plane_helper_disable(plane, NULL);
 	drm_plane_cleanup(plane);
 }