fix_multi_int8 (#42977)

paddle/fluid/framework/ir/multihead_matmul_fuse_pass.cc

@@ -864,7 +864,7 @@ int MultiHeadMatmulV2FusePass::BuildFusionV2(Graph* graph,
     auto* mul0_op_desc = mul0->Op();
 
     // all mul op has same input.
-    if (multihead_op_desc.HasAttr("Input_scale")) {
+    if (mul0_op_desc->HasAttr("Input_scale")) {
       multihead_op_desc.SetAttr("Input_scale",
                                 mul0_op_desc->GetAttr("Input_scale"));
     }