bonding: drop unused to_dev macro in bond_sysfs.c

to_dev is not used anymore so drop it.
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_sysfs.c

@@ -42,7 +42,6 @@
 
 #include <net/bonding.h>
 
-#define to_dev(obj)	container_of(obj, struct device, kobj)
 #define to_bond(cd)	((struct bonding *)(netdev_priv(to_net_dev(cd))))
 
 /* "show" function for the bond_masters attribute.