drm/i915: Update a couple of hangcheck comments to talk about engines

We still have lots of comments that refer to the old ring when we mean
struct intel_engine_cs and its hardware correspondence. This patch fixes
an instance inside hangcheck to talk about engines.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-10-git-send-email-chris@chris-wilson.co.uk


Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469606850-28659-5-git-send-email-chris@chris-wilson.co.uk