ioengines: don't record issue_time if ioengines already do it

ioengines: don't record issue_time if ioengines already do it

io_uring, io_uring_cmd, and libaio record issue_time inside the ioengine
code when their commit functions are called. So we don't need to record
issue_time again for these ioengines in td_io_queue.

If we do fill issue_time twice, then mean(slat) + mean(clat) !=
mean(lat):

user@ubuntu:~/fio-dev$ fio-canonical/fio --name=test --ioengine=io_uring --number_ios=1 --rw=randread --size=1M
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=1
fio-3.30-48-g26fa
Starting 1 process

test: (groupid=0, jobs=1): err= 0: pid=172145: Mon Jun  6 16:12:42 2022
  read: IOPS=1000, BW=4000KiB/s (4096kB/s)(4096B/1msec)
    slat (nsec): min=61424, max=61424, avg=61424.00, stdev= 0.00
    clat (nsec): min=242709, max=242709, avg=242709.00, stdev= 0.00
     lat (nsec): min=308346, max=308346, avg=308346.00, stdev= 0.00

61424 + 242709 = 304133 != 308346

If we fill issue_time only once, then the equality will hold (as it
should):

user@ubuntu:~/fio-dev$ fio-latency/fio --name=test --ioengine=io_uring --number_ios=1 --rw=randread --size=1M
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=1
fio-3.30-48-g26fa-dirty
Starting 1 process

test: (groupid=0, jobs=1): err= 0: pid=172220: Mon Jun  6 16:12:47 2022
  read: IOPS=1000, BW=4000KiB/s (4096kB/s)(4096B/1msec)
    slat (nsec): min=53701, max=53701, avg=53701.00, stdev= 0.00
    clat (nsec): min=259566, max=259566, avg=259566.00, stdev= 0.00
     lat (nsec): min=313267, max=313267, avg=313267.00, stdev= 0.00

53701 + 259566 = 313267

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
Link: https://lore.kernel.org/r/20220614155822.307771-3-vincent.fu@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>