drm/i915/guc: Remove obsolete comments and remove unused variable

Originally removed in:
c1adab970348 ("drm/i915/guc: Remove failed doorbell stat from debugfs")
f1448a62a103 ("drm/i915/guc: Remove last submission result from debugfs")

Were accidentally restored in:
925344ccc91d ("BackMerge tag 'v4.12-rc5' into drm-next")

We can also remove unused variable and replace it with a WARN.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170914083216.10192-1-michal.winiarski@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -601,7 +601,6 @@ static void __i915_guc_submit(struct drm_i915_gem_request *rq)
 	struct intel_guc *guc = &rq->i915->guc;
 	struct i915_guc_client *client = guc->execbuf_client;
 	unsigned long flags;
-	int b_ret;
 
 	/* WA to flush out the pending GMADR writes to ring buffer. */
 	if (i915_vma_is_map_and_fenceable(rq->ring->vma))
@@ -610,7 +609,7 @@ static void __i915_guc_submit(struct drm_i915_gem_request *rq)
 	spin_lock_irqsave(&client->wq_lock, flags);
 
 	guc_wq_item_append(client, rq);
-	b_ret = guc_ring_doorbell(client);
+	WARN_ON(guc_ring_doorbell(client));
 
 	client->submissions[engine_id] += 1;
 

drivers/gpu/drm/i915/intel_uc.h

@@ -59,10 +59,6 @@ struct drm_i915_gem_request;
  *                available in the work queue (note, the queue is shared,
  *                not per-engine). It is OK for this to be nonzero, but
  *                it should not be huge!
- *   b_fail: failed to ring the doorbell. This should never happen, unless
- *           somehow the hardware misbehaves, or maybe if the GuC firmware
- *           crashes? We probably need to reset the GPU to recover.
- *   retcode: errno from last guc_submit()
  */
 struct i915_guc_client {
 	struct i915_vma *vma;