lmkd: Close cgroup.event_control file when done writing

(cherry pick from commit 1bd2fc4f)

After events are specified by writing into cgroup.event_control file
the file should be closed.

Change-Id: Id015e6a7bac2b74bbc8d8793c85f529ee00bdf55
Merged-In: Id015e6a7bac2b74bbc8d8793c85f529ee00bdf55
Signed-off-by: Suren Baghdasaryan <surenb@google.com>