We used to do it for every queue, which was duplicate work as pstate is
per-device. It could also cause trouble when multiple hw_ctx are created as
the call will succeed for only one of them and the rest will return -EBUSY.
Simplify and fix this by only setting for the first non-null hw_ctx.
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17541>