clippy: fix struct_field_names lint

[xtqqczze]

https://rust-lang.github.io/rust-clippy/master/index.html#struct_field_names

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/pr/bounded-memory. tests/pr/bounded-memory is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/tail/truncate. tests/tail/truncate is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/factor/t34 is no longer failing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!