Jason,

This is hardly a deal breaker. The inspector admits that it was (and may
still be) acceptable practice to use PVC. He would prefer that it be another
material but that's just a personal opinion. The T&P valve is a fail-safe
and is not normally used. It is more than likely that no action on your part
is needed until the water heater is replaced. My advice is leave it alone
and don't worry about it. This is not a big deal.

Dave M.