audio policy: use audio_devices_t when appropriate

Change-Id: I1b3a5879e81c789fb53d356af3d3a1ee2dca955f
diff --git a/include/media/IAudioPolicyService.h b/include/media/IAudioPolicyService.h
index bdd7747..04c927a 100644
--- a/include/media/IAudioPolicyService.h
+++ b/include/media/IAudioPolicyService.h
@@ -79,7 +79,7 @@
                                           int *index,
                                           audio_devices_t device) = 0;
     virtual uint32_t getStrategyForStream(audio_stream_type_t stream) = 0;
-    virtual uint32_t getDevicesForStream(audio_stream_type_t stream) = 0;
+    virtual audio_devices_t getDevicesForStream(audio_stream_type_t stream) = 0;
     virtual audio_io_handle_t getOutputForEffect(effect_descriptor_t *desc) = 0;
     virtual status_t registerEffect(effect_descriptor_t *desc,
                                     audio_io_handle_t io,