drm/amd/powerplay: OD setting fix on Vega10

gfxclk for OD setting is limited to 1980M for non-acg
ASICs of Vega10

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>