Use -Werror in frameworks/av

* Suppress unused-variable warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Exempt-From-Owner-Approval: already had multiple +2 votes
Change-Id: I985f9328684df501b5934a5c01f783ed7ca5aa0c
diff --git a/drm/common/Android.bp b/drm/common/Android.bp
index 0098c89..1552c3f 100644
--- a/drm/common/Android.bp
+++ b/drm/common/Android.bp
@@ -33,6 +33,8 @@
         "ReadWriteUtils.cpp",
     ],
 
+    cflags: ["-Wall", "-Werror"],
+
     static_libs: ["libbinder"],
 
     export_include_dirs: ["include"],