lavfi/join: make use of AVFILTER_DEFINE_CLASS

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/af_join.c

@@ -77,12 +77,7 @@ static const AVOption join_options[] = {
     { NULL },
 };
 
-static const AVClass join_class = {
-    .class_name = "join filter",
-    .item_name  = av_default_item_name,
-    .option     = join_options,
-    .version    = LIBAVUTIL_VERSION_INT,
-};
+AVFILTER_DEFINE_CLASS(join);
 
 static int filter_frame(AVFilterLink *link, AVFrame *frame)
 {