bonding: remove bond_resend_igmp_join_requests read_unlock leftover

After commit 4aa5dee4 ("net: convert resend IGMP to notifier event") we
have 1 read_unlock in bond_resend_igmp_join_requests which isn't paired
with a read_lock because it's removed by that commit.
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -739,7 +739,6 @@ static void bond_resend_igmp_join_requests(struct bonding *bond)
 		queue_delayed_work(bond->wq, &bond->mcast_work, HZ/5);
 	}
 	write_unlock_bh(&bond->curr_slave_lock);
-	read_unlock(&bond->lock);
 }
 
 static void bond_resend_igmp_join_requests_delayed(struct work_struct *work)