[MTD] Fix length comparison in MEMREADOOB

The ops.len member is not initialized, because it is unused for this
operation. The length check needs to use ops.ooblen instead
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/mtdchar.c

@@ -553,7 +553,7 @@ static int mtd_ioctl(struct inode *inode, struct file *file,
 		ops.datbuf = NULL;
 		ops.mode = MTD_OOB_PLACE;
 
-		if (ops.ooboffs && ops.len > (mtd->oobsize - ops.ooboffs))
+		if (ops.ooboffs && ops.ooblen > (mtd->oobsize - ops.ooboffs))
 			return -EINVAL;
 
 		ops.oobbuf = kmalloc(buf.length, GFP_KERNEL);