Fix hack/update-codegen.sh failed to generates the code in right place

[RainbowMango]

When I try to fix issue #30, I found the hack/update-codegen.sh actually not working.

It will generates the files at repo/sigs.k8s.io/... instead of repo/pkg/....

-bash-5.0# hack/update-codegen.sh 
Generating deepcopy funcs
Generating clientset at sigs.k8s.io/work-api/pkg/client/clientset
Generating listers at sigs.k8s.io/work-api/pkg/client/listers
Generating informers at sigs.k8s.io/work-api/pkg/client/informers
Generating register at sigs.k8s.io/work-api/pkg/apis/v1alpha1
-bash-5.0# git status
On branch master
Your branch is up to date with 'origin/master'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	sigs.k8s.io/

nothing added to commit but untracked files present (use "git add" to track)

[k8s-ci-robot]

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This pull-request has been approved by: RainbowMango

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[RainbowMango]

/hold
wait for #32

[RainbowMango]

/hold cancel
cc @qiujian16 @mikeshng

[qiujian16]

/lgtm