Fix 'make code-generation' error

[ashahba]

While running make code-generation I ran into this error:

$ make code-generation 
./hack/update-codegen.sh
mv: cannot stat '/go/src/k8s.io/code-generator': No such file or directory
Makefile:47: recipe for target 'code-generation' failed
make: *** [code-generation] Error 1

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @ashahba. Thanks for your PR.

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