drivers: cpuidle: lpm_levels: Correctly update lpm stats

Correctly update LPM stats for cluster level to indicate
success. Update system_pm_ops as well to use correct exit
status for rpmh master stats update.

Change-Id: Ia50dcb21cd041db0ed17d25897fe346afe06dab2
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>