drm/amdgpu: remove ASD ucode init for dimgrey_cavefish

dimgrey_cavefish has no ASD ucode currently, remove its initialization.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Jack Gui <Jack.Gui@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>