vhost/vsock: Fix error handling in vhost_vsock_init()

A problem about modprobe vhost_vsock failed is triggered with the
following log given:

modprobe: ERROR: could not insert 'vhost_vsock': Device or resource busy

The reason is that vhost_vsock_init() returns misc_register() directly
without checking its return value, if misc_register() failed, it returns
without calling vsock_core_unregister() on vhost_transport, resulting the
vhost_vsock can never be installed later.
A simple call graph is shown as below:

 vhost_vsock_init()
   vsock_core_register() # register vhost_transport
   misc_register()
     device_create_with_groups()
       device_create_groups_vargs()
         dev = kzalloc(...) # OOM happened
   # return without unregister vhost_transport

Fix by calling vsock_core_unregister() when misc_register() returns error.

Fixes: 433fc58e6b ("VSOCK: Introduce vhost_vsock.ko")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Message-Id: <20221108101705.45981-1-yuancan@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vhost/vsock.c

@@ -959,7 +959,14 @@ static int __init vhost_vsock_init(void)
 				  VSOCK_TRANSPORT_F_H2G);
 	if (ret < 0)
 		return ret;
-	return misc_register(&vhost_vsock_misc);
+
+	ret = misc_register(&vhost_vsock_misc);
+	if (ret) {
+		vsock_core_unregister(&vhost_transport.transport);
+		return ret;
+	}
+
+	return 0;
 };
 
 static void __exit vhost_vsock_exit(void)