mem-cache: Fix MRU rebase

Rebase of MRU missed a const qualifier, introducing a compilation
error.

Change-Id: Ia25aa30523613a1a87593a353abe439946656f63
Reviewed-on: https://gem5-review.googlesource.com/9301
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/replacement_policies/mru_rp.cc

@@ -56,7 +56,7 @@ MRURP::reset(CacheBlk *blk)
 }
 
 CacheBlk*
-MRURP::getVictim(ReplacementCandidates& candidates)
+MRURP::getVictim(const ReplacementCandidates& candidates)
 {
     // There must be at least one replacement candidate
     assert(candidates.size() > 0);

src/mem/cache/replacement_policies/mru_rp.hh

@@ -77,7 +77,7 @@ class MRURP : public BaseReplacementPolicy
      * @param cands Replacement candidates, selected by indexing policy.
      * @return Cache block to be replaced.
      */
-    CacheBlk* getVictim(ReplacementCandidates& candidates) override;
+    CacheBlk* getVictim(const ReplacementCandidates& candidates) override;
 };
 
 #endif // __MEM_CACHE_REPLACEMENT_POLICIES_MRU_RP_HH__