drm/i915: Propagate error from completed fences

We need to preserve fatal errors from fences that are being terminated
as we hook them up.

Fixes: ef46884 ("drm/i915: Propagate fence errors")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200506162136.3325-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -1034,8 +1034,10 @@ i915_request_await_request(struct i915_request *to, struct i915_request *from)
 	GEM_BUG_ON(to == from);
 	GEM_BUG_ON(to->timeline == from->timeline);
 
-	if (i915_request_completed(from))
+	if (i915_request_completed(from)) {
+		i915_sw_fence_set_error_once(&to->submit, from->fence.error);
 		return 0;
+	}
 
 	if (to->engine->schedule) {
 		ret = i915_sched_node_add_dependency(&to->sched, &from->sched);