drm/amd/powerplay: convert the sclk/mclk into Mhz for comparation

Convert the clocks into right Mhz unit. Otherwise, it will miss
the equal situation.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>