v3dv: fix base slice selection for copies involving 3D images

For 3D images we should take the slice to copy from or to, from
the Z coordinate of the corresponding offset, not the base array
layer.

Fixes VK_KHR_maintenance1 tests:
dEQP-VK.api.copy_and_blit.core.image_to_image.3d_images.3d_to_2d_by_slices
dEQP-VK.api.copy_and_blit.core.image_to_image.3d_images.2d_to_3d_by_layers

Reviewed-by: Alejandro PiƱeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7364>
1 file changed