adjust to vmod_priv methods

Ref:
https://github.com/varnishcache/varnish-cache/commit/681c11998ec56dc4460a30585210f95a7850ea3b

src/vdfp_pipe.c

@@ -728,6 +728,12 @@ task_free(void *p)
 		free(task->argv);
 }
 
+static const struct vmod_priv_methods priv_task_methods[1] = {{
+		.magic = VMOD_PRIV_METHODS_MAGIC,
+		.type = "vmod_pipe_priv_task",
+		.fini = task_free
+}};
+
 static struct task_cfg *
 get_task(VRT_CTX, struct VPFX(pipe_vdp) *obj, const char *method)
 {
@@ -743,7 +749,7 @@ get_task(VRT_CTX, struct VPFX(pipe_vdp) *obj, const char *method)
 			return (NULL);
 		}
 		priv->len = sizeof(*task);
-		priv->free = task_free;
+		priv->methods = priv_task_methods;
 		task = (struct task_cfg *)priv->priv;
 		INIT_OBJ(task, PIPE_TASK_MAGIC);
 	}