drm/amdgpu: Fix documentaion for amdgpu_bo_add_to_shadow_list

make htmldocs complaints about parameter for amdgpu_bo_add_to_shadow_list

./drivers/gpu/drm/amd/amdgpu/amdgpu_object.c:739: warning: Excess function parameter 'bo' description in 'amdgpu_bo_add_to_shadow_list'
./drivers/gpu/drm/amd/amdgpu/amdgpu_object.c:739: warning: Function parameter or member 'vmbo' not described in 'amdgpu_bo_add_to_shadow_list'
./drivers/gpu/drm/amd/amdgpu/amdgpu_object.c:739: warning: Excess function parameter 'bo' description in 'amdgpu_bo_add_to_shadow_list'

Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>