FdtLib: fdt_rw.c - fix undefined pointer overflow behavior

[antklein]

Description

This change implements a fix for CodeQL issue: https://codeql.github.com/codeql-query-help/cpp/cpp-pointer-overflow-check/ It removes the potential for pointer overflow behavior.

• [ ] Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• [x] Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• [ ] Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

• I validated the CI build tests continue to pass. I also validated the change via QEMU emulation.

Integration Instructions

N/A

[leiflindholm]

Getting rid of this relic of a module is way overdue, so thank you for nudging me to tidy up my work-in-progress and raise #10968. But I don't want to give anyone the impression that this unmaintained component is anything else.

[github-actions[bot]]

This PR has been automatically marked as stale because it has not had activity in 60 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions.

[mergify[bot]]

PR can not be merged due to conflict. Please rebase and resubmit

[leiflindholm]

The EmbeddedPkg libfdt semi-wrapper was deleted by 030d01f80046.