drm: fix missing doc v2

flags is new param for drm_syncob_find_fence, so need update doc, reproduce: make htmldocs

reported:
htmldocs: drivers/gpu/drm/drm_syncobj.c:230: warning: Function parameter or member 'flags' not described in 'drm_syncobj_find_fence'

v2: rebased
Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181017070318.15483-1-david1.zhou@amd.com

drivers/gpu/drm/drm_syncobj.c

@@ -214,6 +214,7 @@ static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
  * @file_private: drm file private pointer
  * @handle: sync object handle to lookup.
  * @point: timeline point
+ * @flags: DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT or not
  * @fence: out parameter for the fence
  *
  * This is just a convenience function that combines drm_syncobj_find() and