drm/i915: Drop assertion that active->fence is unchanged

We cannot assert the fence is not yet changed as the next thread may
change it prior to acquiring our lock.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200225082233.274530-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_active.c

@@ -823,7 +823,6 @@ __i915_active_fence_set(struct i915_active_fence *active,
 		__list_del_entry(&active->cb.node);
 		spin_unlock(prev->lock); /* serialise with prev->cb_list */
 	}
-	GEM_BUG_ON(rcu_access_pointer(active->fence) != fence);
 	list_add_tail(&active->cb.node, &fence->cb_list);
 	spin_unlock_irqrestore(fence->lock, flags);