Use -Werror in hardware/interfaces

* Use hidl_defaults, which has -Wall -Werror.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ifbca0e176a8e031acc27256eb46d23b89cdf1a0e
diff --git a/soundtrigger/2.0/default/Android.mk b/soundtrigger/2.0/default/Android.mk
index 068c6b4..9262858 100644
--- a/soundtrigger/2.0/default/Android.mk
+++ b/soundtrigger/2.0/default/Android.mk
@@ -23,6 +23,8 @@
 LOCAL_SRC_FILES := \
     SoundTriggerHalImpl.cpp
 
+LOCAL_CFLAGS := -Wall -Werror
+
 LOCAL_SHARED_LIBRARIES := \
         libhidlbase \
         libhidltransport \