sysctl: s390 Use the compat_sys_sysctl

Now that we have a generic 32bit compatibility implementation
there is no need for s390 to implement it's own.

Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>