fix the build

Fix the build for platforms using legacy audio_policy.conf file
broken by commit 5a2b6298.

Change-Id: Icb9c8027b1a8163d19162f311ec1364da7383a2c
diff --git a/services/audiopolicy/common/managerdefinitions/src/StreamDescriptor.cpp b/services/audiopolicy/common/managerdefinitions/src/StreamDescriptor.cpp
index 359e473..b3019e1 100644
--- a/services/audiopolicy/common/managerdefinitions/src/StreamDescriptor.cpp
+++ b/services/audiopolicy/common/managerdefinitions/src/StreamDescriptor.cpp
@@ -26,6 +26,7 @@
 
 #include "StreamDescriptor.h"
 #include "Gains.h"
+#include "policy.h"
 #include <utils/Log.h>
 #include <utils/String8.h>