avfilter/af_volume: Don't free options manually

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/af_volume.c

@@ -127,7 +127,6 @@ static av_cold void uninit(AVFilterContext *ctx)
 {
     VolumeContext *vol = ctx->priv;
     av_expr_free(vol->volume_pexpr);
-    av_opt_free(vol);
     av_freep(&vol->fdsp);
 }