Fix issue 1743700: AudioTrack: setPlaybackRate can not set the playback rate to twice of the ouputSR

Store sample rate on 32 bits instead of 16 bits in audio_track_cblk_t.
Removed sampleRate() methods from AudioTrack and AudioRecord: replaced by getSampleRate().
AudioTrack::setSampleRate() no returns a status.
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index ba0467c..7c86a65 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -201,7 +201,6 @@
     /* getters, see constructor */
 
             int         streamType() const;
-            uint32_t    sampleRate() const;
             int         format() const;
             int         channelCount() const;
             uint32_t    frameCount() const;
@@ -246,7 +245,7 @@
 
     /* set sample rate for this track, mostly used for games' sound effects
      */
-            void        setSampleRate(int sampleRate);
+            status_t    setSampleRate(int sampleRate);
             uint32_t    getSampleRate();
 
     /* Enables looping and sets the start and end points of looping.