block: rsxx: fix error return code of rsxx_pci_probe()

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>

drivers/block/rsxx/core.c

@@ -871,6 +871,7 @@ static int rsxx_pci_probe(struct pci_dev *dev,
 	card->event_wq = create_singlethread_workqueue(DRIVER_NAME"_event");
 	if (!card->event_wq) {
 		dev_err(CARD_TO_DEV(card), "Failed card event setup.\n");
+		st = -ENOMEM;
 		goto failed_event_handler;
 	}