nvmet: replace white spaces with tabs

Instead of the using the whitespaces use tab spacing in the
nvmet_execute_identify_ns().

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>