bonding: fix compile error if debug enabled

This is what I get if debug is enabled:

drivers/net/bonding/bond_ipv6.c: In function 'bond_na_send':
drivers/net/bonding/bond_ipv6.c:75: error: 'slave' undeclared (first use in this function)
drivers/net/bonding/bond_ipv6.c:75: error: (Each undeclared identifier is reported only once
drivers/net/bonding/bond_ipv6.c:75: error: for each function it appears in.)

This patch fixes that.
Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_ipv6.c

@@ -75,7 +75,7 @@ static void bond_na_send(struct net_device *slave_dev,
 	addrconf_addr_solict_mult(daddr, &mcaddr);
 
 	dprintk("ipv6 na on slave %s: dest %pI6, src %pI6\n",
-	       slave->name, &mcaddr, daddr);
+	       slave_dev->name, &mcaddr, daddr);
 
 	skb = ndisc_build_skb(slave_dev, &mcaddr, daddr, &icmp6h, daddr,
 			      ND_OPT_TARGET_LL_ADDR);