cpu: fix RetiredStores probe point
cpu: fix RetiredStores probe point

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
(transplanted from 43e80296995dbbbae094be0d1da68152bc084048)

andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin