drm/amdgpu: fix dpm bug on Kv.

1. current_ps/request_ps not update.
2. compare crrent_ps and request_ps, if same,
   don't re-set power state.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>