drm/amd/powerplay: refine code in cz_smumgr.c

cz_smu_init will be called in sw_init.
so it should not touch other blocks's
firmware as they were not ready.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>