drm/amd/powerplay: valid Vega10 DPMTABLE_OD_UPDATE_VDDC settings V2

With user specified voltage(DPMTABLE_OD_UPDATE_VDDC), the AVFS
will be disabled. However, the buggy code makes this actually not
working as expected.

- V2: clear all OD flags excpet DPMTABLE_OD_UPDATE_VDDC

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