[PATCH] nvmet: fix nvme status code when namespace is disabled

[Jirong Feng]

> Jirong Feng, can you please re-run the test as requested and verify
> that the I/O error goes away. If so, please reply with your "Tested-by"
> tag.

Having re-runned the test basing on kernel 6.9.0-rc5, the error does go 
away.

Tested-by: Jirong Feng <jirong.feng at easystack.cn>