[PATCH] nvme: check ctrl.tagset before start ns scan

[Sagi Grimberg]

Hi Jianchao,

> ctrl.tagset maybe NULL due to failure of io queue setup or blk-mq
> tagset allocation in nvme_reset_work. Then panic would come up.
> To fix this, just add ctrl.tagset check in nvme_scan_work.

This came up before (and forgotten...) I think we should not
have state indicators other than ctrl->state.

How about instead we add a new state NVME_CTRL_ADMIN_LIVE when we have
no I/O queues.