The roqIdx produced by storeQueue may not always be older than roq
since store instructions writeback to store queue and roq at the same cycle.
After that, if roq commits some instructions after the store, roqIdx given by Roq
will be older than that given by the store queue.
Thus, we set valid for roq.io.commitRoqIndex when roq is not in walking
to ensure that roq always gives the oldest roqIdx