[Fc Fusion] fix fc fusion duplicative arguments bug test=develop (#2135)

lite/core/mir/fusion/fc_fuser.cc

@@ -61,6 +61,8 @@ void FcFuser::InsertNewNode(SSAGraph* graph, const key2nodes_t& matched) {
 
 cpp::OpDesc FcFuser::GenOpDesc(const key2nodes_t& matched) {
   cpp::OpDesc op_desc = *matched.at("mul")->stmt()->op_info();
+  op_desc.mutable_inputs()->clear();
+  op_desc.mutable_outputs()->clear();
   op_desc.SetType("fc");
   op_desc.SetInput("Input", {matched.at("x")->arg()->name});
   op_desc.SetInput("W", {matched.at("W")->arg()->name});