drm_aux-dev: fix error handling in drm_dp_aux_dev_init()

If class_create() fails, there is no need for class_destroy().

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1467237135-13075-1-git-send-email-khoroshilov@ispras.ru

drivers/gpu/drm/drm_dp_aux_dev.c

@@ -355,8 +355,7 @@ int drm_dp_aux_dev_init(void)
 
 	drm_dp_aux_dev_class = class_create(THIS_MODULE, "drm_dp_aux_dev");
 	if (IS_ERR(drm_dp_aux_dev_class)) {
-		res = PTR_ERR(drm_dp_aux_dev_class);
-		goto out;
+		return PTR_ERR(drm_dp_aux_dev_class);
 	}
 	drm_dp_aux_dev_class->dev_groups = drm_dp_aux_groups;