avfilter/avf_showfreqs: fix check for failed allocation

libavfilter/avf_showfreqs.c

@@ -195,7 +195,7 @@ static int config_output(AVFilterLink *outlink)
     if (!s->fft_data)
         return AVERROR(ENOMEM);
     s->avg_data = av_calloc(s->nb_channels, sizeof(*s->avg_data));
-    if (!s->fft_data)
+    if (!s->avg_data)
         return AVERROR(ENOMEM);
     for (i = 0; i < s->nb_channels; i++) {
         s->fft_data[i] = av_calloc(s->win_size, sizeof(**s->fft_data));