drm/udl: Remove unused field dev from struct udl_device

Reduce the size of struct udl_device by removing the unused
field dev.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://lore.kernel.org/r/20250410105948.25463-2-tzimmermann@suse.de