disp: msm: sde: delay cwb done wait for last frame

Commit Ifa100424733 ("disp: msm: sde: delay
encoder disable for clone mode") delays the CWB
encoder disable but it is also skipping the CWB
disable flush. That can cause the underrun on dp
display if it uses the same 3d_merge HW block. This
change reverts the portion of original code and
only delays the last cwb frame done wait. It still
keep the last CWB frame done wait as it is if crtc
is also moving to inactive state.

Change-Id: I3461188a35197f2925899ceea7ef705adf00a398
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>