drm/i915/guc: Initialise doorbell cookie to matching value

Set the initial value of the doorbell cookie from the client.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161129121024.22650-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -134,8 +134,8 @@ static int guc_update_doorbell_id(struct intel_guc *guc,
 
 	/* Activate the new doorbell */
 	__set_bit(new_id, doorbell_bitmap);
-	doorbell->cookie = 0;
 	doorbell->db_status = GUC_DOORBELL_ENABLED;
+	doorbell->cookie = client->doorbell_cookie;
 	return guc_allocate_doorbell(guc, client);
 }