staging: drm/omap: avoid multiple planes having same z-order

Multiple video pipes on same output with same z-order is an undefined
behavior.  Set a unique z-order value based on overlay number/id.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/omapdrm/omap_plane.c

@@ -439,7 +439,7 @@ struct drm_plane *omap_plane_init(struct drm_device *dev,
 	if (priv)
 		omap_plane->info.zorder = 0;
 	else
-		omap_plane->info.zorder = 1;
+		omap_plane->info.zorder = ovl->id;
 
 	update_manager(plane);