audio: Access header files through header libs

Access header files through header libs which are not accessed
directly.

Change-Id: Ia98e31fd43d56e9bb4786ee00de49961047808d4
diff --git a/hal/Android.mk b/hal/Android.mk
index 51f758e..ae8dd5a 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -61,6 +61,8 @@
 
 LOCAL_CFLAGS += -Wno-macro-redefined
 
+LOCAL_HEADER_LIBRARIES := libhardware_headers
+
 LOCAL_SRC_FILES := \
 	audio_hw.c \
 	voice.c \
@@ -74,7 +76,7 @@
 LOCAL_C_INCLUDES += $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ/usr/techpack/audio/include
 LOCAL_ADDITIONAL_DEPENDENCIES += $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ/usr
 ifneq ($(filter msmnile,$(TARGET_BOARD_PLATFORM)),)
-  LOCAL_HEADER_LIBRARIES := audio_kernel_headers
+  LOCAL_HEADER_LIBRARIES += audio_kernel_headers
 endif
 ifneq ($(filter sdm670 qcs605 msmnile,$(TARGET_BOARD_PLATFORM)),)
   LOCAL_C_INCLUDES += $(TARGET_OUT_INTERMEDIATES)/vendor/qcom/opensource/audio-kernel/include