Fix window_stride calculation in DALI pipeline & Fix dither generatio…
…n (#2858)

Signed-off-by: Joaquin Anton <janton@nvidia.com>

Co-authored-by: Somshubra Majumdar <titu1994@gmail.com>
(cherry picked from commit 6987b6cfc9c9769f61116d0ac5a49088798266f8)