Use -Werror in hardware/interfaces

* Remove unused local variables.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I48dbbf670cc9eeff2391983788983420f8547cc9
diff --git a/audio/common/2.0/default/Android.bp b/audio/common/2.0/default/Android.bp
index 0486a5c..7fab220 100644
--- a/audio/common/2.0/default/Android.bp
+++ b/audio/common/2.0/default/Android.bp
@@ -15,6 +15,7 @@
 
 cc_library_shared {
     name: "android.hardware.audio.common@2.0-util",
+    defaults: ["hidl_defaults"],
     vendor_available: true,
     srcs: [
         "EffectMap.cpp",