That assumes people were going to break the law in the first place by speeding... you can't be guilty of the crime of not helping someone else commit a crime.
Maybe if they had some way to prove that you knew it would help them avoid police in order to speed... but that seems like a pretty high bar of evidence would be required (and they would have to attempt to go after you in the first place).
>Reporting on the presence on police is protected first amendment activity
Waze has had a way to report speed traps for years. Where are those subpoenas? That at least is a loss of revenue.
This also assumes that this can be traced back to whoever reported it in the app, and it would be trivial just simply not log any PII on that