USB: cdc-acm: more sanity checking

An attack has become available which pretends to be a quirky
device circumventing normal sanity checks and crashes the kernel
by an insufficient number of interfaces. This patch adds a check
to the code path for quirky devices.

Signed-off-by: Oliver Neukum <ONeukum@suse.com>
CC: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
static void acm_tty_cleanup(struct tty_struct *tty)
{
	struct acm *acm = tty->driver_data;
	dev_dbg(&acm->control->dev, "%s\n", __func__);
	tty_port_put(&acm->port);
}

static void acm_tty_cleanup(struct tty_struct *tty)
{
	struct acm *acm = tty->driver_data;
	dev_dbg(&acm->control->dev, "%s\n", __func__);
	tty_port_put(&acm->port);
}
