drm/i915: Don't die in wait_for_pending_flips

We can apperently miss them, but breaking the entire driver hampers
testing. So bail out after one minute, our customerary "this is a lost
cause" timeout.

References: https://bugs.freedesktop.org/show_bug.cgi?id=78383Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3274,8 +3274,9 @@ static void intel_crtc_wait_for_pending_flips(struct drm_crtc *crtc)
 
 	WARN_ON(waitqueue_active(&dev_priv->pending_flip_queue));
 
-	wait_event(dev_priv->pending_flip_queue,
-		   !intel_crtc_has_pending_flip(crtc));
+	WARN_ON(wait_event_timeout(dev_priv->pending_flip_queue,
+				   !intel_crtc_has_pending_flip(crtc),
+				   60*HZ) == 0);
 
 	mutex_lock(&dev->struct_mutex);
 	intel_finish_fb(crtc->primary->fb);