[bufferization] Simplify code. NFCI.

        return callOp->emitError() << "expected a CallOp";

      func::FuncOp calledFunction = getCalledFunction(callOp);

      assert(calledFunction && "could not retrieved called func::FuncOp");

      auto it = callerMap.try_emplace(calledFunction, DenseSet<Operation *>{});

      it.first->getSecond().insert(callOp);

      if (calledBy[calledFunction].count(funcOp) == 0) {

        calledBy[calledFunction].insert(funcOp);

      callerMap[calledFunction].insert(callOp);

      if (calledBy[calledFunction].insert(funcOp).second) {

        numberCallOpsContainedInFuncOp[funcOp]++;

      }

      return WalkResult::advance();