Do not warn about ignored warnings

Change warning level from Wno-error to Wno, since we ignore these
warnings in external projects.

Test: m
Change-Id: Iffedaca0d2f83a186d10fdcd87045a1a98cdc701
diff --git a/sources.bp b/sources.bp
index 8c7f886..4e29880 100644
--- a/sources.bp
+++ b/sources.bp
@@ -27,8 +27,8 @@
         "-DUSE_OPENSSL_PBKDF2",
         "-Wall",
         "-Werror",
-        "-Wno-error=implicit-function-declaration",
-        "-Wno-error=unused-variable",
+        "-Wno-implicit-function-declaration",
+        "-Wno-unused-variable",
     ],
 
     export_include_dirs: [