avcodec/tta: Use av_freep() to avoid leaving stale pointers in memory

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

libavcodec/tta.c

@@ -394,7 +394,7 @@ static av_cold int tta_decode_close(AVCodecContext *avctx) {
     TTAContext *s = avctx->priv_data;
 
     if (s->bps < 3)
-        av_free(s->decode_buffer);
+        av_freep(&s->decode_buffer);
     s->decode_buffer = NULL;
     av_freep(&s->ch_ctx);