drm/msm/sde: fix kickoff ref count for single phys encoder usecase

The pending_kickoff ref count is not updated properly
for single physical encoder usecase resulting in frame-done
triggered prematurely, causing various issues. Update the
ref count during kickoff so that the frame-done and fences
for the frame are handled properly.

Change-Id: I6d62b047905c27cd5f039b83e9d490378b603714
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>