message: Make `Transpose` device compatible.
  The transpose is still built on host.
diff: @@ -3380,9 +3380,9 @@ SparseMatrix *Transpose (const SparseMatrix &A)
  m = A.Height(); // number of rows of A
  n = A.Width(); // number of columns of A
  nnz = A.NumNonZeroElems();
  - A_i = A.GetI();
  - A_j = A.GetJ();
  - A_data = A.GetData();
  + A_i = A.HostReadI();
  + A_j = A.HostReadJ();
  + A_data = A.HostReadData();
  At_i = Memory<int>(n+1);
  At_j = Memory<int>(nnz);
  