Fix a typo in the sample code

Change-Id: I27ee1b0ef8abf5decefae1ec1706a9f142016344
diff --git a/media/java/android/media/MediaExtractor.java b/media/java/android/media/MediaExtractor.java
index 4b8d3cb..749ef12 100644
--- a/media/java/android/media/MediaExtractor.java
+++ b/media/java/android/media/MediaExtractor.java
@@ -45,7 +45,7 @@
  * }
  * ByteBuffer inputBuffer = ByteBuffer.allocate(...)
  * while (extractor.readSampleData(inputBuffer, ...) >= 0) {
- *   int trackIndex = extractor.getTrackIndex();
+ *   int trackIndex = extractor.getSampleTrackIndex();
  *   long presentationTimeUs = extractor.getSampleTime();
  *   ...
  *   extractor.advance();