Fix media-s-sources visibility

Prevent sources from being leaked elsewhere.

Test: m
Bug: 177640454
Change-Id: I5ff9e8542746b912b618af5b7756d975cdad13ea

apex/media/service/Android.bp

@@ -23,10 +23,10 @@ package {
 filegroup {
     name: "service-media-s-sources",
     srcs: [
-      "java/**/*.java",
+        "java/**/*.java",
     ],
     path: "java",
-    visibility: ["//frameworks/base/services"], // TODO(b/177640454): Should be private.
+    visibility: ["//visibility:private"],
 }
 
 java_sdk_library {