power: don't wait for timeout if sys_sync completes early

In some cases the suspend thread is waiting for timer to expire
even if the sync workqueue is empty. So the suspend is taking extra
time.
To avoid this waiting, sending the completion event from
last sync item in workqueue.

CRs-Fixed: 583016

Change-Id: Ia3219e90762ec7f6ad3e7096126832acfd03ed69
Signed-off-by: Srinivasarao P <spathi@codeaurora.org>

idea is taken here - https://github.com/rmbq/android_kernel_htc_msm8960/commit/ded5f7c29701a95cb84e327a719b3b744f329c81