nvme-trace: fix cdw10 buffer overrun

The field is defined to be a 24 byte array, we don't need to multiply
the sizeof() that field by the number of dwords it covers.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>