cdrom: fix improper type cast, which can leat to information leak.

There is another cast from unsigned long to int which causes
a bounds check to fail with specially crafted input. The value is
then used as an index in the slot array in cdrom_slot_status().

This issue is similar to CVE-2018-16658 and CVE-2018-10940.

Signed-off-by: Young_X <YangX92@hotmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
static int cdrom_ioctl_select_speed(struct cdrom_device_info *cdi,
		unsigned long arg)
{
	cd_dbg(CD_DO_IOCTL, "entering CDROM_SELECT_SPEED\n");

	if (!CDROM_CAN(CDC_SELECT_SPEED))
		return -ENOSYS;
	return cdi->ops->select_speed(cdi, arg);
}

static int cdrom_ioctl_select_speed(struct cdrom_device_info *cdi,
		unsigned long arg)
{
	cd_dbg(CD_DO_IOCTL, "entering CDROM_SELECT_SPEED\n");

	if (!CDROM_CAN(CDC_SELECT_SPEED))
		return -ENOSYS;
	return cdi->ops->select_speed(cdi, arg);
}
