drm/i915/guc: Replace preempt_client lookup with engine->preempt_context

Circumvent the dance we currently perform to find the preempt_client and
lookup its HW context for this engine, as we know we have already pinned
the preempt_context on the engine.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190408091728.20207-15-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_guc_submission.c

@@ -567,7 +567,7 @@ static void inject_preempt_context(struct work_struct *work)
 					     preempt_work[engine->id]);
 	struct intel_guc_client *client = guc->preempt_client;
 	struct guc_stage_desc *stage_desc = __get_stage_desc(client);
-	struct intel_context *ce = intel_context_lookup(client->owner, engine);
+	struct intel_context *ce = engine->preempt_context;
 	u32 data[7];
 
 	if (!ce->ring->emit) { /* recreate upon load/resume */