drm/amd/powerplay: fix bugs of checking if dpm is running on Tonga

Fixes OD failures on Tonga.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>