zbd: use zone_lock() in zbd_process_swd()

zbd: use zone_lock() in zbd_process_swd()

Most of ZBD code in fio uses zone_lock() to lock write pointer zones.
This wrapper, besides doing the obvious pthread mutex lock, quiesce
the outstanding i/o when running via asynchronous ioengines. This is
necessary to avoid deadlocks. The function zbd_process_swd(), however,
still uses the naked pthread mutex to lock zones and this leads to a
deadlock when running ZBD test #48 against regular nullb devices.

The fix added in the same patch series that introduced test #48 was to
NOT initialize SWD at all, but this solution is found to create
problems with verify. As the proper fix, modify zbd_process_swd()
to use zone_lock(). This makes the test #48 pass even when SWD counter
is initialized.

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>