[PATCH net-next] failover: Add missing check to validate 'slave_dev' in net_failover_slave_unregister

[YueHaibing]

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/net_failover.c: In function 'net_failover_slave_unregister':
drivers/net/net_failover.c:598:35: warning:
 variable 'primary_dev' set but not used [-Wunused-but-set-variable]

There should check the validity of 'slave_dev'.

Fixes: cfc80d9a1163 ("net: Introduce net_failover driver")
Suggested-by: Samudrala, Sridhar <sridhar.samudr...@intel.com>
Signed-off-by: YueHaibing <yuehaib...@huawei.com>
---
 drivers/net/net_failover.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/net_failover.c b/drivers/net/net_failover.c
index 7ae1856..af1ece8 100644
--- a/drivers/net/net_failover.c
+++ b/drivers/net/net_failover.c
@@ -602,6 +602,9 @@ static int net_failover_slave_unregister(struct net_device 
*slave_dev,
        nfo_info = netdev_priv(failover_dev);
        primary_dev = rtnl_dereference(nfo_info->primary_dev);
        standby_dev = rtnl_dereference(nfo_info->standby_dev);
+
+       if (slave_dev != primary_dev && slave_dev != standby_dev)
+               return -ENODEV;
 
        vlan_vids_del_by_dev(slave_dev, failover_dev);
        dev_uc_unsync(slave_dev, failover_dev);