drm/amd/powerplay: do the comparison in the right Khz granularity

Convert the operands on the two sides into the same granularity.

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>