Add actually correct rXXXXX here.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@22810 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/APIchanges

@@ -12,7 +12,7 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
-2010-04-01 - rxxxxx - lavf 52.61.0 - metadata API
+2010-04-01 - r22806 - lavf 52.61.0 - metadata API
   Add a flag for av_metadata_set2() to disable overwriting of
   existing tags.