drm/udl: Use the drm_driver.dumb_destroy default

drm_gem_dumb_destroy() is the drm_driver.dumb_destroy default,
so no need to set it.

Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1502034068-51384-9-git-send-email-noralf@tronnes.org

drivers/gpu/drm/udl/udl_drv.c

@@ -54,7 +54,6 @@ static struct drm_driver driver = {
 
 	.dumb_create = udl_dumb_create,
 	.dumb_map_offset = udl_gem_mmap,
-	.dumb_destroy = drm_gem_dumb_destroy,
 	.fops = &udl_driver_fops,
 
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,