[triton][NFC] Refactor build function of ScanOp (#5861)

It's better to use ScanOp's build function to replace ReduceOp's.

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lib/Dialect/Triton/IR/Ops.cpp

@@ -551,10 +551,9 @@ unsigned ReduceOp::getNumOperands() { return this->getOperands().size(); }
 void ScanOp::build(OpBuilder &builder, OperationState &state,
                    ValueRange operands, int axis, bool reverse) {
   SmallVector<Type> inferredReturnTypes;
-  state.addAttribute("reverse", builder.getBoolAttr(reverse));
   for (auto arg : operands)
     inferredReturnTypes.push_back(arg.getType());
-  ReduceOp::build(builder, state, inferredReturnTypes, operands, axis);
+  ScanOp::build(builder, state, inferredReturnTypes, operands, axis, reverse);
 }
 
 LogicalResult