There were two issues:
1. The global_work_offset parameter is optional but we errored on NULL
2. We didn't return the reqd_work_group_size when set on the kernel.
Fixes: 376d1e6667 ("rusticl: implement cl_khr_suggested_local_work_size")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38375>