authPrompt: Properly get oVirt service name
Commit 809f820c moved the definition of OVIRT_SERVICE_NAME to 'js/gdm/oVirt.js' but missed updating one occurrence. This commit fixes it.
Commit 809f820c moved the definition of OVIRT_SERVICE_NAME to 'js/gdm/oVirt.js' but missed updating one occurrence. This commit fixes it.