Use audio_format_t consistently

Was int, uint32_t, uint16_t, and uint8_t with 2-bit bitfield.
Also replace 0 by AUDIO_FORMAT_DEFAULT and replace 1 by
AUDIO_FORMAT_PCM_16_BIT.

Change-Id: Ia8804f53f1725669e368857d5bb2044917e17975
diff --git a/core/jni/android_media_AudioTrack.cpp b/core/jni/android_media_AudioTrack.cpp
index 2573aa6d..b1cbf1d 100644
--- a/core/jni/android_media_AudioTrack.cpp
+++ b/core/jni/android_media_AudioTrack.cpp
@@ -240,7 +240,7 @@
 
     // compute the frame count
     int bytesPerSample = audioFormat == javaAudioTrackFields.PCM16 ? 2 : 1;
-    int format = audioFormat == javaAudioTrackFields.PCM16 ? 
+    audio_format_t format = audioFormat == javaAudioTrackFields.PCM16 ?
             AUDIO_FORMAT_PCM_16_BIT : AUDIO_FORMAT_PCM_8_BIT;
     int frameCount = buffSizeInBytes / (nbChannels * bytesPerSample);