[mlir] Use llvm::less_first (NFC) (#136398)

Author: kazutakahirata

mlir/lib/Dialect/SparseTensor/Transforms/Utils/LoopEmitter.cpp

@@ -352,8 +352,7 @@ void LoopEmitter::initSubSectIterator(OpBuilder &builder, Location loc) {
     if (depRedOrder.empty())
       continue;
 
-    std::sort(depRedOrder.begin(), depRedOrder.end(),
-              [](auto &l, auto &r) { return std::get<0>(l) < std::get<0>(r); });
+    llvm::sort(depRedOrder, llvm::less_first());
 
     SmallVector<SparseIterator *> lastIter(tensors.size(), nullptr);
     for (auto [loop, t, lvl] : depRedOrder) {