drm/amd/powerplay: round up the Mhz convertion (v2)

Since the clock value there may be like 29999 10Khz.

v2: rebase (Alex)

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>