nvmet: fix error handling in nvmet_execute_identify_cns_cs_ns()

nvmet: fix error handling in nvmet_execute_identify_cns_cs_ns()

Nvme specifications state that:

If the I/O Command Set associated with the namespace identified by the
NSID field does not support the Identify Namespace data structure
specified by the CSI field, the controller shall abort the command with
a status code of Invalid Field in Command.

In other words, if nvmet_execute_identify_cns_cs_ns() is called for a
target with a block device that is not zoned, we should not return any
data and set the status to NVME_SC_INVALID_FIELD.

While at it, it is also better to revalidate the ns block devie *before*
checking if the block device is zoned, to ensure that
nvmet_execute_identify_cns_cs_ns() operates against updated device
characteristics.

Fixes: aaf2e048af27 ("nvmet: add ZBD over ZNS backend support")
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>