block/rnbd-srv: no need to check sess_dev

Check ret is enough since if sess_dev is NULL which also
implies ret should be 0.
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Link: https://lore.kernel.org/r/20230524070026.2932-5-guoqing.jiang@linux.devSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-srv.c

@@ -96,7 +96,7 @@ rnbd_get_sess_dev(int dev_id, struct rnbd_srv_session *srv_sess)
 		ret = kref_get_unless_zero(&sess_dev->kref);
 	rcu_read_unlock();
 
-	if (!sess_dev || !ret)
+	if (!ret)
 		return ERR_PTR(-ENXIO);
 
 	return sess_dev;