Revert 190c462d..bf3012ad"

I shouldn't have pushed this, CI was right - I failed to remove the
BUG_ON(!ops->wait);

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>