Use av_freep intead of av_free to free pointers in vp56 context.

Originally committed as revision 21395 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vp56.c

@@ -687,9 +687,9 @@ av_cold int vp56_free(AVCodecContext *avctx)
 {
     VP56Context *s = avctx->priv_data;
 
-    av_free(s->above_blocks);
-    av_free(s->macroblocks);
-    av_free(s->edge_emu_buffer_alloc);
+    av_freep(&s->above_blocks);
+    av_freep(&s->macroblocks);
+    av_freep(&s->edge_emu_buffer_alloc);
     if (s->framep[VP56_FRAME_GOLDEN]->data[0])
         avctx->release_buffer(avctx, s->framep[VP56_FRAME_GOLDEN]);
     if (s->framep[VP56_FRAME_GOLDEN2]->data[0])