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

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

libavfilter/vf_kerndeint.c

@@ -63,7 +63,7 @@ static av_cold void uninit(AVFilterContext *ctx)
 {
     KerndeintContext *kerndeint = ctx->priv;
 
-    av_free(kerndeint->tmp_data[0]);
+    av_freep(&kerndeint->tmp_data[0]);
 }
 
 static int query_formats(AVFilterContext *ctx)