RDMA/ocrdma: Remove a unused-label warning

If IPV6 is disabled, we get the warning:

    drivers/infiniband/hw/ocrdma/ocrdma_main.c:650:1: warning: label ‘err_notifier6’ defined but not used [-Wunused-label]
Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/ocrdma/ocrdma_main.c

@@ -656,8 +656,10 @@ static int __init ocrdma_init_module(void)
 	return 0;
 
 err_be_reg:
+#if IS_ENABLED(CONFIG_IPV6)
 	ocrdma_unregister_inet6addr_notifier();
 err_notifier6:
+#endif
 	ocrdma_unregister_inetaddr_notifier();
 	return status;
 }