avformat/hlsplaylist: add missing header includes

Fixes checkheaders.
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/hlsplaylist.h

@@ -23,7 +23,11 @@
 #ifndef AVFORMAT_HLSPLAYLIST_H
 #define AVFORMAT_HLSPLAYLIST_H
 
+#include <stdint.h>
+
 #include "libavutil/common.h"
+#include "avformat.h"
+#include "avio.h"
 
 typedef enum {
     PLAYLIST_TYPE_NONE,