KVM: s390: fix diagnose code extraction

commit 743db27c526e0f31cc507959d662e97e2048a86f upstream.

The diagnose code to be used is the contents of the base register (if not
zero), plus the displacement. The current code ignores the base register
contents. So let's fix that...

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>