message: fix the set_zero grid problem
diff: @@ -204,10 +204,10 @@ void spmv(std::shared_ptr<const CudaExecutor> exec,
  const matrix::Coo<ValueType, IndexType> *a,
  const matrix::Dense<ValueType> *b, matrix::Dense<ValueType> *c)
  {
  - auto nnz = a->get_num_stored_elements();
  + auto nnz = c->get_num_stored_elements();
  const dim3 grid(ceildiv(nnz, default_block_size));
  const dim3 block(default_block_size);
  - set_zero<<<grid, block>>>(c->get_num_stored_elements(),
  + set_zero<<<grid, block>>>(nnz,
  as_cuda_type(c->get_values()));
  spmv2(exec, a, b, c);
  