Remove trailing \0 from values read from ppc64le device-tree.

[dberg1]

Values in Power OF device-tree are null-terminated. For example:

$ sudo od -t cx1 /proc/device-tree/system-id
0000000   I   B   M   ,   0   6   7   8   B   2   3   0   0  \0
         49  42  4d  2c  30  36  37  38  42  32  33  30  30  00

The null character needs to be trimmed or otherwise it will be part of the Go string.
This is causing problems with node attribute systemUUID in Kubernetes/OpenShift clusters for ppc64le nodes:

# kubectl get node master-0 -o yaml
 ...
  nodeInfo:
    architecture: ppc64le
    bootID: dab6f6ac-7d18-4411-9b87-9bd990752071
    containerRuntimeVersion: cri-o://1.19.1-7.rhaos4.6.git6377f68.el8
    kernelVersion: 4.18.0-193.41.1.el8_2.ppc64le
    kubeProxyVersion: v1.19.0+1833054
    kubeletVersion: v1.19.0+1833054
    machineID: 5884c39c43a843d78f6051c8485e376a
    operatingSystem: linux
    osImage: Red Hat Enterprise Linux CoreOS 46.82.202101270839-0 (Ootpa)
    systemUUID: "IBM,0678B22C0\0"

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[k8s-ci-robot]

Hi @dberg1. Thanks for your PR.

I'm waiting for a google 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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[iwankgb]

/ok-to-test

[dberg1]

@googlebot I signed it!

[google-cla]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

---

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Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

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[dberg1]

@googlebot I signed it!

[iwankgb]

LGTM

[bobbypage]

LGTM thanks!