drm/amd/pm: Fix DPM level count on aldebaran

Firmware returns zero-based max level, increment by one to get
total levels. This fixes the issue of not showing all levels and current
frequency when frequency is at max DPM level.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>