drm/amdgpu: add hub->ctx_distance in setup_vmid_config

add hub->ctx_distance when read CONTEXT1_CNTL, align w/
write back operation.

v2: fix coding style errors reported by checkpatch.pl (Christian)

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Lang Yu <lang.yu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>