hal: Fix warnings in audio HAL and policy

Enable Wall and Werror and fix warnings in
HAL and policy manager

CRs-Fixed: 962049

Change-Id: Ie93c8f933943875ac68e8318d777602ed864f531
diff --git a/hal/voice.c b/hal/voice.c
index b10de17..d1db987 100644
--- a/hal/voice.c
+++ b/hal/voice.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2015, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2013-2016, The Linux Foundation. All rights reserved.
  * Not a contribution.
  *
  * Copyright (C) 2013 The Android Open Source Project
@@ -276,12 +276,12 @@
     return call_state;
 }
 
-bool voice_is_in_call(struct audio_device *adev)
+bool voice_is_in_call(const struct audio_device *adev)
 {
     return adev->voice.in_call;
 }
 
-bool voice_is_in_call_rec_stream(struct stream_in *in)
+bool voice_is_in_call_rec_stream(const struct stream_in *in)
 {
     bool in_call_rec = false;