avdevice/dv1394: Use av_freep() to avoid leaving stale pointers in memory

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

libavdevice/dv1394.c

@@ -206,7 +206,7 @@ static int dv1394_close(AVFormatContext * context)
         av_log(context, AV_LOG_ERROR, "Failed to munmap DV1394 ring buffer: %s\n", strerror(errno));
 
     close(dv->fd);
-    av_free(dv->dv_demux);
+    av_freep(&dv->dv_demux);
 
     return 0;
 }