Change NBAIO_Format from typedef to struct

This will make it easier to support arbitrary sample rates,
channel counts, and sample formats in NBAIO.

Change-Id: I5eda412648b094358f5eefc38300e9ec8a734cd3
diff --git a/include/media/nbaio/NBAIO.h b/include/media/nbaio/NBAIO.h
index 468508c..4150a09 100644
--- a/include/media/nbaio/NBAIO.h
+++ b/include/media/nbaio/NBAIO.h
@@ -52,7 +52,10 @@
 // the combinations that are actually needed within AudioFlinger.  If the list of combinations grows
 // too large, then this decision should be re-visited.
 // Sample rate and channel count are explicit, PCM interleaved 16-bit is assumed.
-typedef unsigned NBAIO_Format;
+struct NBAIO_Format {
+//private:
+    unsigned    mPacked;
+};
 
 extern const NBAIO_Format Format_Invalid;