remove references to PWM_MULTICHAN option

[raiden00pl]

Summary

remove references to PWM_MULTICHAN option

Impact

apps part to apache/nuttx#18864

Testing

CI

[xiaoxiang781216]

@raiden00pl fix the style:

    1: .codespellrc
Error: /home/runner/work/nuttx-apps/nuttx-apps/apps/examples/pwm/pwm_main.c:150:2: error: Bad left brace alignment
Error: /home/runner/work/nuttx-apps/nuttx-apps/apps/examples/pwm/pwm_main.c:167:2: error: Bad right brace alignment

[lupyuen]

Sorry @raiden00pl could you implement retry for NTFC git clone? It failed 4 times today, we're hoping to conserve our precious GitHub Runners whenever git clone fails thanks :-) FYI @simbit18

$ git clone -b release-0.0.1 https://github.com/apache/nuttx-ntfc-testing
fatal: unable to access 'https://github.com/apache/nuttx-ntfc-testing/': The requested URL returned error: 500

• risc-v-01 failed: https://github.com/apache/nuttx-apps/actions/runs/25666748529/job/75355628393#step:10:1
• risc-v-02 failed: https://github.com/apache/nuttx-apps/actions/runs/25666748529/job/75355628706#step:10:1
• sim-01 failed: https://github.com/apache/nuttx-apps/actions/runs/25666748529/job/75355628480#step:10:1
• x86_64-01 failed: https://github.com/apache/nuttx-apps/actions/runs/25666748529/job/75355628367#step:10:1

https://lupyuen.github.io/nuttx-github-jobs/build-monitor

[raiden00pl]

@lupyuen PR is here #3478 but I don't know if this will help in all cases. This is an error on the GitHub infra side. If GitHub is unable to clone from its own repos, it means GitHub is temporarily broken and it may take longer than our repeated attempts.