lavf/rtspcodes: add missing header include

Fixes make checkheaders
Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rtspcodes.h

@@ -24,6 +24,8 @@
 #ifndef AVFORMAT_RTSPCODES_H
 #define AVFORMAT_RTSPCODES_H
 
+#include "libavutil/common.h"
+
 /** RTSP handling */
 enum RTSPStatusCode {
 RTSP_STATUS_CONTINUE             =100,