drm/doc: Fix typos for early_unregister doc

There's no late_unregister. While at it switch to the new canonical
reference style.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170125062657.19270-14-daniel.vetter@ffwll.ch

include/drm/drm_crtc.h

@@ -560,7 +560,7 @@ struct drm_crtc_funcs {
 	 *
 	 * This optional hook should be used to unregister the additional
 	 * userspace interfaces attached to the crtc from
-	 * late_unregister(). It is called from drm_dev_unregister(),
+	 * @late_register. It is called from drm_dev_unregister(),
 	 * early in the driver unload sequence to disable userspace access
 	 * before data structures are torndown.
 	 */

include/drm/drm_encoder.h

@@ -75,7 +75,7 @@ struct drm_encoder_funcs {
 	 *
 	 * This optional hook should be used to unregister the additional
 	 * userspace interfaces attached to the encoder from
-	 * late_unregister(). It is called from drm_dev_unregister(),
+	 * @late_register. It is called from drm_dev_unregister(),
 	 * early in the driver unload sequence to disable userspace access
 	 * before data structures are torndown.
 	 */

include/drm/drm_plane.h

@@ -372,7 +372,7 @@ struct drm_plane_funcs {
 	 *
 	 * This optional hook should be used to unregister the additional
 	 * userspace interfaces attached to the plane from
-	 * late_unregister(). It is called from drm_dev_unregister(),
+	 * @late_register. It is called from drm_dev_unregister(),
 	 * early in the driver unload sequence to disable userspace access
 	 * before data structures are torndown.
 	 */