drm/udl: Call udl_handle_damage() with DRM framebuffer

Simplifying the udl code before replacing struct udl_framebuffer.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114141025.32198-5-tzimmermann@suse.de