drm/msm/sde: fix race condition in client_event_list deregister

In msm_release, there is condition where client_event_list nodes
can be deleted from msm_ioctl_deregister_event, when spin unlock
is called inside client_event_list loop. This change prevents
spin_unlock inside client_event_list loop.

Change-Id: I6b7c4c6113a9fd4698029e91486b16742d5c8b5b
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>