backend: do ioprio_set() before calling the ioengine init callback

backend: do ioprio_set() before calling the ioengine init callback

To be able to report clat stats on a per priority granularity (instead of
only high/low priority), we need to do ioprio_set(), and the matching
td->ioprio assignment, before calling the io engine init callback.

When a thread is using more than a single priority (e.g. option
cmdprio_percentage is used), fio_cmdprio_init() will need to allocate and
initialize an array that will hold the clat stats for all the different
priorities that will be used by the struct td.

For fio_cmdprio_init() to be able to initialize a per priority clat array
properly, we need to assign td->ioprio before calling td_io_init().

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/20220203192814.18552-3-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>