nes: handling failed allocation when creating workqueue

Since create_singlethread_workqueue uses kzalloc internally,
it can fail when the system is under memory pressure, so need
to handle it.

Signed-off-by: Insu Yun <wuninsu@gmail.com>
Reviewed-by: Leon Romanovsky <leon@leon.nu>
Signed-off-by: Doug Ledford <dledford@redhat.com>