Fix secondary coredns missing var

[VannTen]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Unbreak using coredns_dual

Which issue(s) this PR fixes:

Fixes #10816

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Fix secondary coredns missing var 

[floryut]

Duplicate of #10815 let's this if @arusa can fix his CLA

[mzaian]

Thanks a lot @VannTen

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mzaian, VannTen

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[simon-wessel]

@VannTen A near-term patch release for this would be great. The underlying bug breaks cluster DNS during the whole upgrade process.

[VannTen]

You mean including non dual coredns ?

[simon-wessel]

@VannTen This was a wrong assumption on my side, the issue I was talking about is actually #10860