445 remove _input suffix for pwm hwmon duty sources

[codifryed]

Fixes: #445

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Checklist:

• Adhere to the development process
• Conform to the style guide
• Verify that the changes work as expected on real hardware
• Add automated tests cases
• Verify that all (other) automated tests (still) pass
• Update the README and other applicable documentation pages
• Update the liquidctl.8 Linux/Unix/Mac OS man page
• Update or add applicable docs/*guide.md device guides
• Submit relevant data, scripts or dissectors to https://github.com/liquidctl/collected-device-data

[jonasmalacofilho]

Oh, the incorrect behavior is present in the tests as well, due to mocking of sysfs. But I can fix those on my end.

Thanks again!