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/policy_hal/Android.mk b/policy_hal/Android.mk
index 70814d8..811c2c9 100644
--- a/policy_hal/Android.mk
+++ b/policy_hal/Android.mk
@@ -27,6 +27,8 @@
 LOCAL_STATIC_LIBRARIES := \
     libmedia_helper \
 
+LOCAL_CFLAGS += -Wall -Werror
+
 ifeq ($(strip $(AUDIO_FEATURE_ENABLED_VOICE_CONCURRENCY)),true)
 LOCAL_CFLAGS += -DVOICE_CONCURRENCY
 endif