drm/amdgpu: Don't warn for unsupported set_xgmi_plpd_mode

set_xgmi_plpd_mode may be unsupported and this isn't error, no need to
print warning for it.

v2: add ret2 to save the status of psp_ras_trigger_error.

Suggested-by:  <lijo.lazar@amd.com>
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>