tty.c: rename PKT_FLAG_KEY to AV_PKT_FLAG_KEY.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit a9d921cb)

libavformat/tty.c

@@ -120,7 +120,7 @@ static int read_packet(AVFormatContext *avctx, AVPacket *pkt)
     pkt->size = av_get_packet(avctx->pb, pkt, n);
     if (pkt->size <= 0)
         return AVERROR(EIO);
-    pkt->flags |= PKT_FLAG_KEY;
+    pkt->flags |= AV_PKT_FLAG_KEY;
     return 0;
 }