Fix codegen

[liu-cong]

When I ran make generate, I ran into error

./hack/.. script
../code-generator
./hack/update-codegen.sh: line 25: ../code-generator/kube_codegen.sh: No such file or directory

This fix was from the LWS repo: https://github.com/kubernetes-sigs/lws/blob/ed2b1f9848b6f38dfd553ccd838671933a343be5/hack/update-codegen.sh#L23

[k8s-ci-robot]

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[ahg-g]

is this still needed?