drm/msm/sde: check for missed frame done after waiting

Fix disable callflow in sde encoder so that the physical
encoder has a chance to wait for the frame done first, before
the virtual encoder declares an error for a missed frame done
event in the encoder disable case.

Change-Id: Ifc6cad708ad98324eef31435e709ad763059abbf
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>