drm/msm/sde: fix refcount issue with ctl start cnt

For some scenarios HW does not trigger the CTL START
interrupt; in those cases current driver takes care of
signaling the ctl retire fence during the PP DONE irq,
however driver is missing to update the ctl start count.
This fix makes sure driver also updates the ctl start
refcount if the interrupt is not triggered by HW.

Change-Id: I7c8846b95411632e5c2039aca836138c081f785c
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>