nvmet: fix Identify Controller handling

nvmet: fix Identify Controller handling

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

Fixes: ab5d0b38c047 ("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>