net: bonding: remove redudant brackets

It is not necessary to use two brackets. As such, the redudant brackets
are removed.

CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <gospo@cumulusnetworks.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1379,7 +1379,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 	 * the current ifenslave will set the interface down prior to
 	 * enslaving it; the old ifenslave will not.
 	 */
-	if ((slave_dev->flags & IFF_UP)) {
+	if (slave_dev->flags & IFF_UP) {
 		netdev_err(bond_dev, "%s is up - this may be due to an out of date ifenslave\n",
 			   slave_dev->name);
 		res = -EPERM;