Forget to clear the `_ever_prefetched` flag in the CacheBlk::invalidate() function

[Kepontry]

The function clearPrefetched() doesn't clear the _ever_prefetched flag. It seems that here we need a clearEverPrefetched() like function. When that is applied, there is a slight change in scores(<0.02). https://github.com/OpenXiangShan/GEM5/blob/6a85ffb479c8c1ecff432ddd5801216b4e829580/src/mem/cache/cache_blk.hh#L205-L209