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>

drivers/cdrom/cdrom.c

@@ -2445,7 +2445,7 @@ static int cdrom_ioctl_select_disc(struct cdrom_device_info *cdi,
 		return -ENOSYS;
 
 	if (arg != CDSL_CURRENT && arg != CDSL_NONE) {
-		if ((int)arg >= cdi->capacity)
+		if (arg >= cdi->capacity)
 			return -EINVAL;
 	}