util/ra: Sanity check that the driver selected a valid reg.

freedreno was returning -1 when it didn't pick a reg from the given bitset
due to an off-by-a-small-number error.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4537>
1 file changed