Convert struct cred kuids and kgids into userspace uids and gids when
returning them.
These s390 system calls slipped through the cracks in my first
round of converstions :(
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>