drm/amdgpu: query default sclk from smu for cyan_skillfish

Query default sclk instead of hard code.

Signed-off-by: Lang Yu <lang.yu@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>