bonding: fix kstrtou8() return value verification in num_peer_notif

It returns 0 in case of success, !0 error otherwise. Fix the improper error
verification.

Fixes: 2c9839c ("bonding: add num_grat_arp attribute netlink support")
CC: sfeldma@cumulusnetworks.com
CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Acked-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_sysfs.c

@@ -776,7 +776,7 @@ static ssize_t bonding_store_num_peer_notif(struct device *d,
 	int ret;
 
 	ret = kstrtou8(buf, 10, &new_value);
-	if (!ret) {
+	if (ret) {
 		pr_err("%s: invalid value %s specified.\n",
 		       bond->dev->name, buf);
 		return ret;