drm/amd/powerplay: fix compile warning for wrong data type V2

do_div expects the 1st argument in 64bit instead of 32bit.
Drop the usage of do_div as it seems unnecessary.

V2: drop usage of do_div completely

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