scsi: myrb: Fix up null pointer access on myrb_cleanup()

When myrb_probe() fails the callback might not be set, so we need to
validate the 'disable_intr' callback in myrb_cleanup() to not cause a null
pointer exception. And while at it do not call myrb_cleanup() if we cannot
enable the PCI device at all.

Link: https://lore.kernel.org/r/20220523120244.99515-1-hare@suse.de
Reported-by: Zheyu Ma <zheyuma97@gmail.com>
Tested-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/myrb.c

@@ -1239,7 +1239,8 @@ static void myrb_cleanup(struct myrb_hba *cb)
 	myrb_unmap(cb);
 
 	if (cb->mmio_base) {
-		cb->disable_intr(cb->io_base);
+		if (cb->disable_intr)
+			cb->disable_intr(cb->io_base);
 		iounmap(cb->mmio_base);
 	}
 	if (cb->irq)
@@ -3413,9 +3414,13 @@ static struct myrb_hba *myrb_detect(struct pci_dev *pdev,
 	mutex_init(&cb->dcmd_mutex);
 	mutex_init(&cb->dma_mutex);
 	cb->pdev = pdev;
+	cb->host = shost;
 
-	if (pci_enable_device(pdev))
+	if (pci_enable_device(pdev)) {
-		goto failure;
+		dev_err(&pdev->dev, "Failed to enable PCI device\n");
+		scsi_host_put(shost);
+		return NULL;
+	}
 
 	if (privdata->hw_init == DAC960_PD_hw_init ||
 	    privdata->hw_init == DAC960_P_hw_init) {