KVM: s390: cleanup jump lables in kvm_arch_init_vm

As all cleanup functions can handle their respective NULL case
there is no need to have more than one error jump label.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>