Fix CSI ExpandVolume stagingPath

[Crypto89]

Description

Fix the checking of the staging path against the mountRoot on the host rather then checking against the containerMountPoint which (probably) never exists on the host causing it to default back the the legacy behaviour.

Testing & Reproduction steps

Should be easily reproducible on any csi driver supporting ExpandVolume and has nomad namespaces enabled. Tested with nomad enterprise 1.8.5

Links

#24465

Contributor Checklist

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Reviewer Checklist

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[hashicorp-cla-app]

All committers have signed the CLA.