Fixes gcc '-Wunused-but-set-variable' warning:
drivers/xen/pvcalls-back.c: In function 'pvcalls_sk_state_change':
drivers/xen/pvcalls-back.c:286:28: warning:
 variable 'intf' set but not used [-Wunused-but-set-variable]
It not used since 
e6587cdbd732 ("pvcalls-back: set -ENOTCONN in
pvcalls_conn_back_read")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
 
 static void pvcalls_sk_state_change(struct sock *sock)
 {
        struct sock_mapping *map = sock->sk_user_data;
-       struct pvcalls_data_intf *intf;
 
        if (map == NULL)
                return;
 
-       intf = map->ring;
        atomic_inc(&map->read);
        notify_remote_via_irq(map->irq);
 }