drm/exynos: removed pageflip_event_list init code when closed.

if one process is terminated by ctrl-c while two processes are
using pageflip feature then for last pageflip event,
user can't get poll from kernel side so this patch fixes the problem.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyoungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>