s390: show_registers() should not map user space addresses to kernel symbols

It doesn't make sense to map user space addresses to kernel symbols when
show_registers() prints a user space psw. So just skip the translation part
if a user space psw is handled.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>