drm/amd/powerplay: revise calling chain on retrieving frequency range

This helps to maintain clear code layers and drop unnecessary
parameter.

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>