avfilter/vf_unsharp: use av_freep() avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_unsharp.c

@@ -215,7 +215,7 @@ static void free_filter_param(UnsharpFilterParam *fp)
     int z;
 
     for (z = 0; z < 2 * fp->steps_y; z++)
-        av_free(fp->sc[z]);
+        av_freep(&fp->sc[z]);
 }
 
 static av_cold void uninit(AVFilterContext *ctx)