rtsp: kill a pointer type warning (void **) vs. (AVFormatContext **)

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

libavformat/rtsp.c

@@ -617,7 +617,7 @@ int ff_rtsp_open_transport_ctx(AVFormatContext *s, RTSPStream *rtsp_st)
         s->ctx_flags |= AVFMTCTX_NOHEADER;
 
     if (s->oformat && CONFIG_RTSP_MUXER) {
-        int ret = ff_rtp_chain_mux_open(&rtsp_st->transport_priv, s, st,
+        int ret = ff_rtp_chain_mux_open((AVFormatContext **)&rtsp_st->transport_priv, s, st,
                                         rtsp_st->rtp_handle,
                                         RTSP_TCP_MAX_PACKET_SIZE);
         /* Ownership of rtp_handle is passed to the rtp mux context */