use correct src-registry for k8s-staging-coredns
use correct src-registry for k8s-staging-coredns

This was erroneously changed to the wrong source registry in
126c65c335b723f16c76b6e5b38df3e44b558bf8.

thockin/k8s.io,thockin/k8s.io,kubernetes/k8s.io,thockin/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io