staging: lustre: obdclass: return -EFAULT if copy_to_user() fails

We recently changed from using obd_ioctl_popdata() to calling
copy_to_user() directly. This if statement was supposed to be deleted
but it was over looked. "err" is zero at this point so it means we
return success.

Fixes: b03679f6a41a ("staging: lustre: uapi: remove obd_ioctl_popdata() wrapper")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/lustre/lustre/obdclass/class_obd.c

···
 		       dev);
 
 		if (copy_to_user((void __user *)arg, data, sizeof(*data)))
-		if (err)
 			err = -EFAULT;
 		goto out;
 	}