avfilter/edgedetect: reuse already defined ctx.

libavfilter/vf_edgedetect.c

@@ -290,7 +290,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
     AVFilterContext *ctx = inlink->dst;
     EdgeDetectContext *edgedetect = ctx->priv;
-    AVFilterLink *outlink = inlink->dst->outputs[0];
+    AVFilterLink *outlink = ctx->outputs[0];
     int p, direct = 0;
     AVFrame *out;