doxy: move av_guess_sample_aspect_ratio to correct place

It should not be a part of the RIFF FourCCs group.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavformat/avformat.h

@@ -1948,6 +1948,10 @@ const struct AVCodecTag *avformat_get_riff_video_tags(void);
  */
 const struct AVCodecTag *avformat_get_riff_audio_tags(void);
 
+/**
+ * @}
+ */
+
 /**
  * Guesses the sample aspect ratio of a frame, based on both the stream and the
  * frame aspect ratio.
@@ -1967,10 +1971,6 @@ const struct AVCodecTag *avformat_get_riff_audio_tags(void);
  */
 AVRational av_guess_sample_aspect_ratio(AVFormatContext *format, AVStream *stream, AVFrame *frame);
 
-/**
- * @}
- */
-
 /**
  * @}
  */