audio policy: use audio_devices_t when appropriate

Change-Id: I1b3a5879e81c789fb53d356af3d3a1ee2dca955f
diff --git a/services/audioflinger/AudioPolicyService.h b/services/audioflinger/AudioPolicyService.h
index 962c917..e41d51e 100644
--- a/services/audioflinger/AudioPolicyService.h
+++ b/services/audioflinger/AudioPolicyService.h
@@ -95,7 +95,7 @@
                                           audio_devices_t device);
 
     virtual uint32_t getStrategyForStream(audio_stream_type_t stream);
-    virtual uint32_t getDevicesForStream(audio_stream_type_t stream);
+    virtual audio_devices_t getDevicesForStream(audio_stream_type_t stream);
 
     virtual audio_io_handle_t getOutputForEffect(effect_descriptor_t *desc);
     virtual status_t registerEffect(effect_descriptor_t *desc,