io_uring: set async IO priority to td->ioprio in fio_ioring_prep()

io_uring: set async IO priority to td->ioprio in fio_ioring_prep()

The default priority (which is either 0 or the value set by "prio" and
"prioclass" options) is now saved in td->ioprio.

The simplest thing is therefore to unconditionally set the async IO
priority to td->ioprio in fio_ioring_prep(), and let fio_ioring_prio_prep()
only handle the case where cmdprio_percentage/cmdprio_bssplit is enabled.

Therefore, fio_ioring_prio_prep() doesn't need to care if prio/prioclass
was enabled or not, we can simply think that fio_ioring_prio_prep()
might "override" the default priority, whatever the default priority may
be.

Doing it this way also has the advantage that the prio_prep() function
in io_uring will now look identical to the prio_prep() function in
libaio.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20211112095428.158300-5-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>