avformat/tee: flip assigment direction

Found-by: CSA
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/tee.c

@@ -467,7 +467,7 @@ static int tee_write_packet(AVFormatContext *avf, AVPacket *pkt)
         if ((ret = av_copy_packet(&pkt2, pkt)) < 0 ||
             (ret = av_dup_packet(&pkt2))< 0)
             if (!ret_all) {
-                ret = ret_all;
+                ret_all = ret;
                 continue;
             }
         tb  = avf ->streams[s ]->time_base;