This message tells you that the router needed to modify the configured policing rate to be slightly different from what you have configured, because most probably, your configured policing rate would require a degree of timer precision that your router was not capable of providing.
It won't have any impact on the router operation, just the resulting policing rate will be slightly different from what you have configured.
So if I want to stop this message from occurring, what should I do?
Instead of using the original rate in the policing command, use the value the router told you. This will make the router happy and it won't complain about the need to adapt the rate to its own capabilities.