drm/amd/pm: no pptable resetup on runpm exiting

It is assumed the pptable used before runpm is same as
the one used afterwards. Thus, we can reuse the stored
copy and do not need to resetup the pptable again.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Feifei Xu <feifei.xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>