anv: fix acceleration structure descriptor copies

anv: fix acceleration structure descriptor copies

We're not supposed to have a
VkWriteDescriptorSetAccelerationStructureKHR when doing a copy. We
should instead get the acceleration structure object from the source
descriptor.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 03e1e19246da ("anv: Refactor descriptor copy")
Reviewed-by: Rohan Garg <rohan.garg@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15241>