mtd: blktrans: use better error code for unimplemented ioctl()

In commit 50183936254b ("mtd: blktrans: change blktrans_getgeo return
value") we fixed the problem that ioctl(HDIO_GETGEO) might return 0
(success) for mtdblock devices which did not implement the feature and
would leave a blank (zero) result.

But now, let's get the error code right. Other code paths on this ioctl
tend to use -ENOTTY to notify the user that the ioctl() is not supported
for the device, so let's use that instead of -EOPNOTSUPP.

Suggested-by: Richard Weinberger <[e-mail]>
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/mtd_blkdevs.c

···
 	if (!dev->mtd)
 		goto unlock;
 
-	ret = dev->tr->getgeo ? dev->tr->getgeo(dev, geo) : -EOPNOTSUPP;
+	ret = dev->tr->getgeo ? dev->tr->getgeo(dev, geo) : -ENOTTY;
 unlock:
 	mutex_unlock(&dev->lock);
 	blktrans_dev_put(dev);