fix code style

test=develop

paddle/fluid/operators/top_k_op.cc

@@ -31,7 +31,7 @@ class TopkOp : public framework::OperatorWithKernel {
 
     auto input_dims = ctx->GetInputDim("X");
     PADDLE_ENFORCE_EQ(input_dims.size(), 2,
-                    "Rank of TopK op's input must be 2.");
+                      "Rank of TopK op's input must be 2.");
     const int k = static_cast<int>(ctx->Attrs().Get<int>("k"));
 
     PADDLE_ENFORCE_GE(k, 1, "k must >= 1");