drm/i915: Do not record a successful syncpoint for a dma-await

drm/i915: Do not record a successful syncpoint for a dma-await

As we may unwind the requests, even though the request we are awaiting
has a global_seqno that seqno may be revoked during the await and so we
can not reliably use it as a barrier for all future awaits on the same
timeline.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170503093924.5320-6-chris@chris-wilson.co.uk