Fix offload tracks playback

Translation between audio_offload_info_t and AudioOffloadInfo
was missing a field. This was causing compressed tracks to play
using 'deep_buffer' mode instead of 'offload'.

Changing output stream async callback methods to 'oneway',
since they don't require anything from the callee.

Change-Id: I27fe7fb715e421f102db21a10d34e1dc3134cf01
Test: play MP3 file with Play Music, check audioflinger dump
diff --git a/audio/2.0/IStreamOutCallback.hal b/audio/2.0/IStreamOutCallback.hal
index 267c46d..cdb38de 100644
--- a/audio/2.0/IStreamOutCallback.hal
+++ b/audio/2.0/IStreamOutCallback.hal
@@ -23,15 +23,15 @@
     /*
      * Non blocking write completed.
      */
-    onWriteReady();
+    oneway onWriteReady();
 
     /*
      * Drain completed.
      */
-    onDrainReady();
+    oneway onDrainReady();
 
     /*
      * Stream hit an error.
      */
-    onError();
+    oneway onError();
 };