It's the opposite, using personal funds is the crime because it should have been a disclosed campaign contribution. Trump also went through several extra steps of having his lawyer and CFO create shell companies and then funnel payments and kickbacks through them falsifying documents all along the way. I'm assuming the DA of a city can't bring FEC violation charges. The charges will be about all the lying and possibly tax evasion. Things his lawyer and CFO have already been convicted of.