drm/nouveau: fix kerneldoc warnings

kernel test robot complains about missing kerneldoc entries:

  drivers-gpu-drm-nouveau-nvkm-subdev-gsp-r535.c:warning:
    Function-parameter-or-struct-member-gsp-not-described-in-nvkm_gsp_radix3_sg

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240210002900.148982-1-ttabi@nvidia.com