timers: Fix text inconsistencies and spelling

Fix some text for consistency: s/lvl/level/ in a comment and use
correct/full function names in comments.

Correct spelling errors as reported by codespell.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240331172652.14086-7-rdunlap@infradead.org