Minor perf improvements to quantized linear 8 bit shader.

[trivedivivek]

Summary: This diff slightly improves the performance of quantized linear op by reducing few heavy math ops such as mod and divide.

Differential Revision: D66134239

[pytorch-bot[bot]]

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:test_tube: See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/6944

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• [DomainsOnly] Jobs fail with GLIBC version not found

:x: 1 New Failure

As of commit 6f76a0bb6c609b8443008dd750fadeb57f5d338f with merge base bafae87bf539391b8c833cceb909dfc919461480 ():

NEW FAILURE - The following job has failed:

* [Check Labels / Check labels](https://hud.pytorch.org/pr/pytorch/executorch/6944#33291453042) ([gh](https://github.com/pytorch/executorch/actions/runs/11943091956/job/33291453042)) `RuntimeError: Error checking labels: PR does not have required labels`

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This pull request was exported from Phabricator. Differential Revision: D66134239

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D66134239

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D66134239

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D66134239

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D66134239