Fix MediaPlayer#getSelectedTrack javadoc

Test: ./gradlew tipOfTreeDocs
Change-Id: Idad3cc3246346a0667d2228f11cce4cecb997713
diff --git a/media2/player/src/main/java/androidx/media2/player/MediaPlayer.java b/media2/player/src/main/java/androidx/media2/player/MediaPlayer.java
index e17f349..6c20c83 100644
--- a/media2/player/src/main/java/androidx/media2/player/MediaPlayer.java
+++ b/media2/player/src/main/java/androidx/media2/player/MediaPlayer.java
@@ -1918,8 +1918,8 @@
     }
 
     /**
-     * Returns the index of the audio or video track currently selected for playback,
-     * The return value is an index into the array returned by {@link #getTrackInfo()}, and can
+     * Returns the audio or video track currently selected for playback.
+     * The return value is an element in the list returned by {@link #getTrackInfo()}, and can
      * be used in calls to {@link #selectTrack(TrackInfo)}.
      *
      * @param trackType should be one of {@link TrackInfo#MEDIA_TRACK_TYPE_VIDEO} or