drm: don't associate _DRM_DRIVER maps with a master

A driver will use the _DRM_DRIVER map flag to indicate that it wants
to be responsible for removing the map itself, bypassing the DRM's
automagic cleanup code.

Since the multi-master changes this has been broken, resulting in some
drivers having their registers unmapped before it's finished with them.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_bufs.c

@@ -371,7 +371,8 @@ static int drm_addmap_core(struct drm_device * dev, resource_size_t offset,
 	list->user_token = list->hash.key << PAGE_SHIFT;
 	mutex_unlock(&dev->struct_mutex);
 
-	list->master = dev->primary->master;
+	if (!(map->flags & _DRM_DRIVER))
+		list->master = dev->primary->master;
 	*maplist = list;
 	return 0;
 	}