nvmet: fix comment typos in admin-cmd.c

small typos fixed in admin-cmd.c

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>