[MLIR] Apply clang-tidy fixes for performance-unnecessary-copy-initialization in PackAndUnpackPatterns.cpp (NFC)

Author: joker-eph

mlir/lib/Dialect/Linalg/Transforms/PackAndUnpackPatterns.cpp

@@ -348,7 +348,7 @@ struct FoldProducerPackWithConsumerLinalgTransposeOp
     auto innerDimsPos = packOp.getInnerDimsPos();
     auto mixedInnerTiles = packOp.getMixedTiles();
     auto outerDimsPerm = packOp.getOuterDimsPerm();
-    auto transposePerm = maybePerm.value();
+    const auto &transposePerm = maybePerm.value();
     SmallVector<int64_t> newOuterDimsPermVec;
     SmallVector<int64_t> newInnerDimsPosVec;
     SmallVector<OpFoldResult> newMixedInnerTilesVec;