iucv: Convert sk_wmem_alloc accesses to refcount_t.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/iucv/af_iucv.c

@@ -402,7 +402,7 @@ static void iucv_sock_destruct(struct sock *sk)
 	}
 
 	WARN_ON(atomic_read(&sk->sk_rmem_alloc));
-	WARN_ON(atomic_read(&sk->sk_wmem_alloc));
+	WARN_ON(refcount_read(&sk->sk_wmem_alloc));
 	WARN_ON(sk->sk_wmem_queued);
 	WARN_ON(sk->sk_forward_alloc);
 }