drm/amd/pp: Fix OD feature enable failed on Vega10 workstation cards

As hw required, soc clock must large than mclk, So we set max soc
clock to OD Max Memory clk.
But on workstation, vbios do not support OD feature, the OD max memory
clock is equal to 0. In this case, driver can support underclocking.
and set od max memory clock to the value in highest memory dpm level.
So the od max memory clock should be less than highest soc clock.
and driver should not change the soc clock.

caused by commit ca57b9b0a156
("drm/amd/pp: Allow underclocking when od table is empty in vbios")

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>