fix: S3: configure external oscillator correctly (IDFGH-13553)

[2opremio]

Addresses part of #10269

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[songruo]

@2opremio We have fixed the issue in b9c58c5. Please check if you can use external oscillator on current master now. I will close the PR, if it is still a problem, feel free to reopen or create a new issue.

[2opremio]

The PR doesn’t seem to set the right buf value for the external oscillator.