UBI: fix check for "too many bytes"

The comparison from the previous line seems to have been erroneously
(partially) copied-and-pasted onto the next. The second line should be
checking req.bytes, not req.lnum.

Coverity CID #139400

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
[rw: Fixed comparison]
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/cdev.c

@@ -455,7 +455,7 @@ static long vol_cdev_ioctl(struct file *file, unsigned int cmd,
 		/* Validate the request */
 		err = -EINVAL;
 		if (req.lnum < 0 || req.lnum >= vol->reserved_pebs ||
-		    req.bytes < 0 || req.lnum >= vol->usable_leb_size)
+		    req.bytes < 0 || req.bytes > vol->usable_leb_size)
 			break;
 
 		err = get_exclusive(desc);