engines:io_uring: fix clat calculation for sqthread poll

engines:io_uring: fix clat calculation for sqthread poll

When sqthread_poll is specified for io_uring and io_uring_cmd I/O
engines, fio reports garbage value for completion latencies. This is
because the issue time was not recorded. Added a change for that.
On the other hand submission latency for sqthread poll is really just
the time it takes to fill in the SQ ring entries and any syscall
required to wake up the idle kernel thread. So there is really no need
to report those.

This fixes the issue: https://github.com/axboe/fio/issues/1484

Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>