mem-cache: added missing override specifier in BoP

Added missing specifier for various virtual functions.

Change-Id: I41aebb3b76bce6dd3bee21ac0e2b0e52cb90fc80
Reviewed-on: https://gem5-review.googlesource.com/c/16728
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/prefetch/bop.hh

@@ -151,7 +151,7 @@ class BOPPrefetcher : public QueuedPrefetcher
         ~BOPPrefetcher() {}
 
         void calculatePrefetch(const PrefetchInfo &pfi,
-                               std::vector<AddrPriority> &addresses);
+                               std::vector<AddrPriority> &addresses) override;
 };
 
 #endif /* __MEM_CACHE_PREFETCH_BOP_HH__ */