csi: fix volume registration error

[mismithhisler]

Description

Volume registrations were appearing to fail due to returning a nil response object.

Testing & Reproduction steps

Links

Fixes: GH #26581

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Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

[gulducat]

lgtm!

[allisonlarson]

thanks!

[github-actions]

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