[MLIR] [NFC] Buffer placement pass - clang tidy warnings

[bondhugula]

Summary

Add missing const - addresses clang tidy warnings.

mlir/lib/Transforms/BufferPlacement.cpp

if (dominator->getParent() != owner->getParentRegion())
       return &owner->getParentRegion()->front();
     return dominator;
   }
 
   /// Finds correct alloc positions according to the algorithm described at
   /// the top of the file for all alloc nodes that can be handled by this
   /// analysis.
   void placeAllocs() const {
-    for (auto &entry : allocs) {
+    for (const AllocEntry &entry : allocs) {
       Value alloc = entry.allocValue;
       // Get the actual block to place the alloc and get liveness information
       // for the placement block.
       Block *placementBlock = entry.placementBlock;
       // We have to ensure that we place the alloc before its first use in this
       // block.
       const LivenessBlockInfo *livenessInfo =
           liveness.getLiveness(placementBlock);
private:
   /// Finds correct dealloc positions according to the algorithm described at
   /// the top of the file for all alloc nodes and block arguments that can be
   /// handled by this analysis.
   void placeDeallocs() const {
     // Move or insert deallocs using the previously computed information.
     // These deallocations will be linked to their associated allocation nodes
     // since they don't have any aliases that can (potentially) increase their
     // liveness.
-    for (auto &entry : allocs) {
+    for (const AllocEntry &entry : allocs) {
       Value alloc = entry.allocValue;
       auto aliasesSet = aliases.resolve(alloc);
       assert(aliasesSet.size() > 0 && "must contain at least one alias");
 
       // Determine the actual block to place the dealloc and get liveness
       // information.
       Block *placementBlock =
           findCommonDominator(alloc, aliasesSet, postDominators);