RDMA/cma: fix null-ptr-deref Read in cma_cleanup

In cma_init, if cma_configfs_init fails, need to free the
previously memory and return fail, otherwise will trigger
null-ptr-deref Read in cma_cleanup.

cma_cleanup
  cma_configfs_exit
    configfs_unregister_subsystem

Fixes: 045959db ("IB/cma: Add configfs for rdma_cm")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Link: https://lore.kernel.org/r/1566188859-103051-1-git-send-email-zhengbin13@huawei.comSigned-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/cma.c

@@ -4724,10 +4724,14 @@ static int __init cma_init(void)
 	if (ret)
 		goto err;
 
-	cma_configfs_init();
+	ret = cma_configfs_init();
+	if (ret)
+		goto err_ib;
 
 	return 0;
 
+err_ib:
+	ib_unregister_client(&cma_client);
 err:
 	unregister_netdevice_notifier(&cma_nb);
 	ib_sa_unregister_client(&sa_client);