drm/amdgpu: drop fclk/gfxclk ratio setting

Since this is not needed any more on the latest SMC firmware.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>