PCI/MSI: pci-xgene-msi: Fix CPU hotplug registration handling

The conversion to the new hotplug state machine introduced a regression
where a successful hotplug registration would be treated as an error,
effectively disabling the MSI driver forever.

Fix it by doing the proper check on the return value.

Fixes: 9c248f8896e6 ("PCI/xgene-msi: Convert to hotplug state machine")
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Duc Dang <dhdang@apm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: stable@vger.kernel.org

drivers/pci/host/pci-xgene-msi.c

@@ -517,7 +517,7 @@ static int xgene_msi_probe(struct platform_device *pdev)
 
 	rc = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "pci/xgene:online",
 			       xgene_msi_hwirq_alloc, NULL);
-	if (rc)
+	if (rc < 0)
 		goto err_cpuhp;
 	pci_xgene_online = rc;
 	rc = cpuhp_setup_state(CPUHP_PCI_XGENE_DEAD, "pci/xgene:dead", NULL,