drm/udl: don't set drm_device->dev_private

We're mostly there already, just a handful of places that didn't use
the to_udl container_of cast. To make sure no new appear, don't set
->dev_private.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Alexios Zavras <alexios.zavras@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "José Roberto de Souza" <jose.souza@intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Allison Randal <allison@lohutok.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415074034.175360-13-daniel.vetter@ffwll.ch