s390/vmcp: return -ENOTTY for unknown ioctl commands

Return -ENOTTY for unknown ioctl commands instead of
-ENOIOCTLCMD. This isn't that much of difference, since common code
will translate -ENOIOCTLCMD to -ENOTTY anyway, but this way it seems
to be more obvious what is happening (at least to me).
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/vmcp.c

@@ -231,7 +231,7 @@ static long vmcp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return put_user(temp, argp);
 	default:
 		mutex_unlock(&session->mutex);
-		return -ENOIOCTLCMD;
+		return -ENOTTY;
 	}
 }