PackageManagerService: fix StrictMode violation in getFileCrC

E/StrictMode(  915): A resource was acquired at attached stack trace but never released. See java.io.Closeable for information on avoiding resource leaks.
E/StrictMode(  915): java.lang.Throwable: Explicit termination method 'close' not called

Change-Id: I8d68c05f32c0c299e9102ffccfcb4776e21a5b4b