Correct hard coded platform used for building image so arm64 builds work

[et304383]

What type of PR is this? /kind bug

What this PR does / why we need it: Fixes #839

Which issue(s) this PR fixes: Fixes #839

Special notes for your reviewer:

Does this PR introduce a user-facing change?: NONE

[linux-foundation-easycla[bot]]

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Once this PR has been reviewed and has the lgtm label, please assign wongma7 for approval. For more information see the Kubernetes Code Review Process.

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[k8s-ci-robot]

This issue is currently awaiting triage.

If cloud-provider-aws contributors determine this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

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[k8s-ci-robot]

Hi @et304383. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.

[hakman]

/ok-to-test

[hakman]

/release-note-none

[k8s-ci-robot]

@et304383: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cloud-provider-aws-e2e-kubetest2-quick	0cfae7e4951b47636158ccea36a2571a0ad631c6	link	false	/test pull-cloud-provider-aws-e2e-kubetest2-quick
pull-cloud-provider-aws-e2e-kubetest2	0cfae7e4951b47636158ccea36a2571a0ad631c6	link	false	/test pull-cloud-provider-aws-e2e-kubetest2

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository. I understand the commands that are listed [here](https://go.k8s.io/bot-commands).

[et304383]

Closing as not required.