KVM: s390: disable RRBM again

commit b273921356df ("KVM: s390: enable more features that need
no hypervisor changes") also enabled RRBM. Turns out that this
instruction does need some KVM code, so lets disable that bit
again.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Fixes: b273921356df ("KVM: s390: enable more features that need no hypervisor changes")
Message-Id: <1429093624-49611-2-git-send-email-borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>