USB: option: fix port-data abuse

Commit 8b4c6a3a ("USB: option: Use generic USB wwan code")
moved option port-data allocation to usb_wwan_startup but still cast the
port data to the old struct...

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>