patch_grid_size computation in PatchEmbed #9

Hi,

Congrats for your really interesting work. By adapting the code for my data, I noticed that in the PatchEmbed class the patch_grid_size attribute does not take the stride into account. Is that normal ? I was thinking patch_grid would rather be like this:
patch_grid_size = (
(image_HW[0] - patch_HW[0]) // stride_HW[0] + 1,
(image_HW[1] - patch_HW[1]) // stride_HW[1] + 1,
)

By the way, if stride = patch_size it gives the same result and if it is not the case, num_patches is used only for pos_embedding that can be interpolated. So, it is not very important.