USB: serial: option: fix Telit Cinterion FN990A name

The correct name for FN990 is FN990A so use it in order to avoid
confusion with FN990B.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>