drm/amd/powerplay: Fix enum mismatch

In several locations the driver uses AMD_CG_STATE_UNGATE (type enum
amd_clockgating_state) instead of AMD_PG_STATE_UNGATE (type enum
amd_powergating_stat) and vice versa. Both constants have the same
value, so this doesn't cause any problems, but we still want to pass
the correct type.

Fixing the mismatch resolves multiple warnings like this when building
with clang:

drivers/gpu/drm/amd/amdgpu/../powerplay/hwmgr/cz_clockpowergating.c:169:7:
  error: implicit conversion from enumeration type 'enum
  amd_powergating_state' to different enumeration type 'enum
  amd_clockgating_state' [-Werror,-Wenum-conversion]
    AMD_PG_STATE_UNGATE);

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>