drm/udl: introduce a macro to convert dev to udl.

This just makes it easier to later embed drm into udl.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190405031715.5959-3-airlied@gmail.com

drivers/gpu/drm/udl/udl_drv.h

@@ -71,6 +71,8 @@ struct udl_device {
 	atomic_t cpu_kcycles_used; /* transpired during pixel processing */
 };
 
+#define to_udl(x) ((x)->dev_private)
+
 struct udl_gem_object {
 	struct drm_gem_object base;
 	struct page **pages;