USB: cdc-acm: do not log successful probe on later errors

Do not log the successful-probe message until the tty device has been
registered.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210322155318.9837-9-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>