drm/amd/pm: check the return of send smc msg for sienna_cichild

Set smu work laod mask may fail, so check return.

Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>