drm/amd/powerplay: fix save dpm level error for smu

the save dpm level should be save previous dpm profile level,
should not modified by get dpm level function.
eg: default auto
1. auto -> standard ==> dpm_level = standard, save_dpm = auto.
2. standard -> auto ==> dpm_level = auto, save_dpm = standard.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>