KVM: s390: write external damage code on machine checks

Let's also write the external damage code already provided by
struct kvm_s390_mchk_info.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>