[release-1.21] Fix partial cache tail latency by correcting the cache chunk size calc

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #2176

/assign cemakd

Fix partial data cache tail latency by correcting the cache chunk size calc

[tonyzhc]

/lgtm
/approve

[tonyzhc]

/ok-to-test

[sunnylovestiramisu]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: k8s-infra-cherrypick-robot, sunnylovestiramisu, tonyzhc

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[k8s-ci-robot]

@k8s-infra-cherrypick-robot: 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-gcp-compute-persistent-disk-csi-driver-e2e-arm	b585ad7	link	false	/test pull-gcp-compute-persistent-disk-csi-driver-e2e-arm
pull-gcp-compute-persistent-disk-csi-driver-e2e-windows-2019	b585ad7	link	false	/test pull-gcp-compute-persistent-disk-csi-driver-e2e-windows-2019

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