drm/amdgpu: Skip mark offset for high priority rings

Only low priority rings are using chunks to save the offset.
Bypass the mark offset callings from high priority rings.

Signed-off-by: Jiadong Zhu <Jiadong.Zhu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>