drm/amd/powerplay: correct vega12 max num of dpm level

Use MAX_NUM_CLOCKS instead of VG12_PSUEDO* macros for
the max number of dpm levels.

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>