mem-cache: schedule already ready pf next cycle

Fix a bug where a ready prefetch request was not
sent directly because the schedMemSideSendEvent
was not called with the right time.
This fix mimics what is done in recvTimingResp.

Change-Id: Ib11f8003ca1b006d976c8cc8ea541434b8902beb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67473
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

src/mem/cache/base.cc

@@ -464,7 +464,8 @@ BaseCache::recvTimingReq(PacketPtr pkt)
 
     if (prefetcher) {
         // track time of availability of next prefetch, if any
-        Tick next_pf_time = prefetcher->nextPrefetchReadyTime();
+        Tick next_pf_time = std::max(
+                            prefetcher->nextPrefetchReadyTime(), clockEdge());
         if (next_pf_time != MaxTick) {
             schedMemSideSendEvent(next_pf_time);
         }