avfilter/af_extrastereo: Fix shadowed variable

Fixes CID1325675
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_extrastereo.c

@@ -71,7 +71,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
     if (av_frame_is_writable(in)) {
         out = in;
     } else {
-        AVFrame *out = ff_get_audio_buffer(inlink, in->nb_samples);
+        out = ff_get_audio_buffer(inlink, in->nb_samples);
         if (!out) {
             av_frame_free(&in);
             return AVERROR(ENOMEM);