drm/msm/sde: re-init delayed work in sde encoder enable

When multidisplay is enabled, delayed_off_work can be submitted to
different crtc worker thread and violate kernel's rule for delayed
task that work must not be used with >1 worker.

This change will re-initialize the delayed work to allow it submitted
to different worker.

CRs-Fixed: 2267120
Change-Id: I65ff4bc67eed31bdfc86e308a9d8968f46c76b62
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>