rtsp: Fix compiler warning for uninitialized variable

This one won't ever be used uninitialized in practice, but
the compiler doesn't realize it.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtsp.c

@@ -1103,7 +1103,7 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port,
                               int lower_transport, const char *real_challenge)
 {
     RTSPState *rt = s->priv_data;
-    int rtx, j, i, err, interleave = 0;
+    int rtx = 0, j, i, err, interleave = 0;
     RTSPStream *rtsp_st;
     RTSPMessageHeader reply1, *reply = &reply1;
     char cmd[2048];