gallium/u_queue: set num_threads correctly if not all threads start

If i-th thread could not be created it means we have i threads,
not i+1, because we start from 0.

Fixes: 404d0d5 "gallium/u_queue: add an option to have multiple worker threads"
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
1 file changed