msm: mdss: fix secondary ctl flush issue on command mode panels

Starting with patch 2551ce16a5d44a3b03d0885b499924f6d218c78e, msm: mdss:
add async support for hw cursor, flush logic was modifed. However it
introduced an issue where if mixer configuration is skipped then
secondary flush is skipped. This can cause issues. Fix the flush logic
by ensuring that secondary flush is not skipped.

Change-Id: Iee8b9ca80353b2fdb096e64b12c865cd10f0dd08
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>