I'm in full agreement that sexual assault is never the fault of the victim, and is always the fault of the attacker. Eliminating sexual assault at the source of the problem is a good goal, and how a woman dresses or behaves is never the source of the problem.
That said, from the perspective of an individual woman, there simply are things she can do to reduce the chances that she will be a victim. Pretending otherwise for the sake of political correctness? That's patronizing, if you ask me. "Don't dress like a slut" is an asinine thing for a police officer to say to a group of college students, but there's a valid message hidden in his poor choice of words.