drm/stm: Drop drm_vblank_cleanup

Again seems just cargo-culted.

Cc: Yannick Fertre <yannick.fertre@st.com>
Cc: Philippe Cornu <philippe.cornu@st.com>
Acked-by: NPhilippe Cornu <philippe.cornu@st.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170524145212.27837-32-daniel.vetter@ffwll.ch

drivers/gpu/drm/stm/ltdc.c

@@ -1144,8 +1144,6 @@ void ltdc_unload(struct drm_device *ddev)
 
 	DRM_DEBUG_DRIVER("\n");
 
-	drm_vblank_cleanup(ddev);
-
 	if (ldev->panel)
 		drm_panel_detach(ldev->panel);