Use const NBAIO_Format& in parameter lists

This is in preparation for changing the typedef to a struct.

Change-Id: I8d73a6b29580c65105afd78f24db7e2f4a1eb872
diff --git a/media/libnbaio/AudioBufferProviderSource.cpp b/media/libnbaio/AudioBufferProviderSource.cpp
index 74a6fdb..e952a00 100644
--- a/media/libnbaio/AudioBufferProviderSource.cpp
+++ b/media/libnbaio/AudioBufferProviderSource.cpp
@@ -24,7 +24,7 @@
 namespace android {
 
 AudioBufferProviderSource::AudioBufferProviderSource(AudioBufferProvider *provider,
-                                                     NBAIO_Format format) :
+                                                     const NBAIO_Format& format) :
     NBAIO_Source(format), mProvider(provider), mConsumed(0)
 {
     ALOG_ASSERT(provider != NULL);