drm: Clean up drm_dev_unplug

Use drm_dev_unregister to unregister the interfaces, which also allows
us to simplify the open_count == 0 case.
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170802115604.12734-5-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_drv.c

@@ -381,21 +381,12 @@ static void drm_device_set_unplugged(struct drm_device *dev)
  */
 void drm_dev_unplug(struct drm_device *dev)
 {
-	/* for a USB device */
-	if (drm_core_check_feature(dev, DRIVER_MODESET))
-		drm_modeset_unregister_all(dev);
-
-	drm_minor_unregister(dev, DRM_MINOR_PRIMARY);
-	drm_minor_unregister(dev, DRM_MINOR_RENDER);
-	drm_minor_unregister(dev, DRM_MINOR_CONTROL);
+	drm_dev_unregister(dev);
 
 	mutex_lock(&drm_global_mutex);
-
 	drm_device_set_unplugged(dev);
-
-	if (dev->open_count == 0) {
-		drm_put_dev(dev);
-	}
+	if (dev->open_count == 0)
+		drm_dev_unref(dev);
 	mutex_unlock(&drm_global_mutex);
 }
 EXPORT_SYMBOL(drm_dev_unplug);