Use -Werror in hardware/qcom/audio

* Suppress existing warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I389b943471ccdcfc9b7db4411fa3973d77303a27
diff --git a/voice_processing/Android.mk b/voice_processing/Android.mk
index e8878ee..ffe0330 100644
--- a/voice_processing/Android.mk
+++ b/voice_processing/Android.mk
@@ -12,6 +12,12 @@
 LOCAL_SRC_FILES:= \
     voice_processing.c
 
+LOCAL_CFLAGS += \
+    -Wall \
+    -Werror \
+    -Wno-unused-function \
+    -Wno-unused-variable \
+
 LOCAL_C_INCLUDES += \
     $(call include-path-for, audio-effects)