Use -Werror in external/libcups

* Do not use -Wno-error.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Idf13d21003934b5c7e5ff28a1ec0e5e8e55451b3
diff --git a/Android.bp b/Android.bp
index d2471e5..03763d9 100644
--- a/Android.bp
+++ b/Android.bp
@@ -76,10 +76,10 @@
     cflags: [
         "-D_PPD_DEPRECATED=",
         "-Wextra",
+        "-Werror",
         "-Wno-unused-parameter",
         "-Wno-sign-compare",
         "-Wno-missing-field-initializers",
-        "-Wno-error",
         "-Wno-implicit-function-declaration",
     ],