igt/gem_exec_await: Flush the WCB before attempting to queue more work

Ensure that the terminating write into WC-memory is flushed before we
might trigger a wait for ring space.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
1 file changed