s390/compat: fix compat wrappers for process_vm system calls

The compat wrappers incorrectly called the non compat versions of
the system process_vm system calls.

Cc: stable@vger.kernel.org
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>