Use -Werror in hardware/interfaces

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I2b8572a3480434f9dad2ae4f8a608ed82281cc68
diff --git a/contexthub/1.0/default/Android.bp b/contexthub/1.0/default/Android.bp
index 9f5131d..d1db6a6 100644
--- a/contexthub/1.0/default/Android.bp
+++ b/contexthub/1.0/default/Android.bp
@@ -39,6 +39,7 @@
     proprietary: true,
     init_rc: ["android.hardware.contexthub@1.0-service.rc"],
     srcs: ["service.cpp"],
+    cflags: ["-Wall", "-Werror"],
 
     shared_libs: [
         "libbase",