s390/dasd: fix ioctl return value

For unimplemented ioctls the dasd driver should return -ENOTTY.

Reported-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>