drm/amd/powerplay: avoid double check feature enabled

the unforce_dpm_levels doesn't need to check feature enablement.
because the smu_get_dpm_freq_range function has check feature logic.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>