[llvm] [Offload] Add `const` to getInfo and calculateOptimalOccupancy (PR #157488)

[Ross Brunton via llvm-commits]

RossBrunton wrote:

I think I was a bit too eager with this. The device handles are `ur_device_handle_impl_t_ *const` rather than `const ur_device_handle_impl_t_*`.

https://github.com/llvm/llvm-project/pull/157488