hwdummy: update to latest libavcodec

modules/codec/avcodec/hwdummy.c

@@ -145,6 +145,8 @@ static void Close(vlc_va_t *va)
 {
     vlc_va_sys_t *sys = va->sys;
 
+#if (LIBAVCODEC_VERSION_INT < AV_VERSION_INT(55, 13, 0))
     av_freep(&sys->context.bitstream_buffers);
+#endif
     free(sys);
 }