fix minor typos in nvmelatency.bt

[venkatrag1]

1. In nvme_complete_rq, we need to delete @start and @cmd entries for arg0 as key instead of tid
2. In nvme_setup_cmd, the if condition for rq_disk will error out on CentOS 8, unless explicitly compared with 0

Signed-off-by: Venkat Ramesh venkatraghavan@fb.com