drm/amdgpu: correct vmhub index in GMC v10/11

Align with new vmhub definition.

v2: use client_id == VMC to decide vmhub(Hawking)

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>