net: marvell: prestera: Fix return value check in prestera_fib_node_find()

rhashtable_lookup_fast() returns NULL pointer not ERR_PTR(), so
it can return fib_node directly in prestera_fib_node_find().
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220223084954.1771075-1-yangyingliang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/prestera/prestera_router_hw.c

@@ -239,7 +239,7 @@ prestera_fib_node_find(struct prestera_switch *sw, struct prestera_fib_key *key)
 
 	fib_node = rhashtable_lookup_fast(&sw->router->fib_ht, key,
 					  __prestera_fib_ht_params);
-	return IS_ERR(fib_node) ? NULL : fib_node;
+	return fib_node;
 }
 
 static void __prestera_fib_node_destruct(struct prestera_switch *sw,