When create_singlethread_workqueue returns NULL to card->event_wq, no
error return code of rsxx_pci_probe() is assigned.

To fix this bug, st is assigned with -ENOMEM in this case.

Fixes: 8722ff8c ("block: IBM RamSan 70/80 device driver")
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Link: https://lore.kernel.org/r/20210310033017.4023-1-baijiaju1990@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>