drm/i915: Correct a comment about the use of the workqueue.

It isn't used for the hangcheck, which does its work right from the
timer trigger, but hangcheck can lead to error state recording, which
is run off of the workqueue.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_dma.c

@@ -1962,7 +1962,7 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	 * bo.
 	 *
 	 * It is also used for periodic low-priority events, such as
-	 * idle-timers and hangcheck.
+	 * idle-timers and recording error state.
 	 *
 	 * All tasks on the workqueue are expected to acquire the dev mutex
 	 * so there is no point in running more than one instance of the