drm/amdgpu/gfx: fix off by one in rb rework (v2)

When I reworked this code, I messed up num rb count.

v2: use hweight32

Reviewed-by: Ken Wang <Qingquing.Wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
2 files changed