USB: usb_wwan: fix bulk-urb allocation

Make sure we do not allocate urbs if we do not have a bulk endpoint.

Legacy code used incorrect assumption to test for bulk endpoints.

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