drm: Fix syncobj handing of schedule() returning 0

drm: Fix syncobj handing of schedule() returning 0

After schedule() returns 0, we must do one last check of COND to
determine the reason for the wakeup with 0 jiffies remaining before
reporting the timeout -- otherwise we may lose the signal due to
scheduler delays.

References: https://bugs.freedesktop.org/show_bug.cgi?id=106690
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180920200530.2836-2-chris@chris-wilson.co.uk
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>