ata: libata-eh: queue hotplug work on the system_dfl_long_wq workqueue

ata: libata-eh: queue hotplug work on the system_dfl_long_wq workqueue

ata_scsi_port_error_handler() uses schedule_delayed_work() to queue
the ap->hotplug_task work.

schedule_delayed_work() always uses the system_percpu_wq per-cpu
workqueue.

ata_scsi_scan_host() queues the ap->hotplug_task work on the unbound
system_dfl_long_wq workqueue.

It seems counter-intuitive to queue the same work on two different
workqueues. Thus, change ata_scsi_port_error_handler() to also queue
the ap->hotplug_task work on the system_dfl_long_wq workqueue, such
that the work is always queued on the same workqueue.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>