util/u_queue: Ensure num_cpu_mask_bits is valid

util/u_queue: Ensure num_cpu_mask_bits is valid

I noticed that we were hitting this before st_create_context() called
util_cpu_detect() and so num_cpu_mask_bits was zero.  But there is no
harm in calling util_cpu_detect(), so lets just call it here to be safe.

Fixes: d877451b48a ("util/u_queue: add UTIL_QUEUE_INIT_SET_FULL_THREAD_AFFINITY")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9266>