net: wan: sbni: fix device usage count

dev_get_by_name() will increment the usage count if the matching device
is found. But we were not decrementing the count if we have got the
device and the device is non-active.
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wan/sbni.c

@@ -1358,6 +1358,8 @@ sbni_ioctl( struct net_device  *dev,  struct ifreq  *ifr,  int  cmd )
 		if( !slave_dev  ||  !(slave_dev->flags & IFF_UP) ) {
 			netdev_err(dev, "trying to enslave non-active device %s\n",
 				   slave_name);
+			if (slave_dev)
+				dev_put(slave_dev);
 			return  -EPERM;
 		}