nvmet: fix Identify Active Namespace ID list handling

The identify command with cns set to NVME_ID_CNS_NS_ACTIVE_LIST does
not depend on the command set. The execution of this command should
thus not look at the csi field specified in the command. Simplify
nvmet_execute_identify() to directly call
nvmet_execute_identify_nslist() without the csi switch-case.

Fixes: ab5d0b38 ("nvmet: add Command Set Identifier support")
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Tested-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>