powerpc/pseries/msi: Fix NULL pointer dereference at irq domain teardown

pseries_msi_ops_teardown() reads pci_dev* from msi_alloc_info_t. However,
pseries_msi_ops_prepare() does not populate this structure, thus it is all
zeros. Consequently, pseries_msi_ops_teardown() triggers a NULL pointer
dereference crash.

struct pci_dev is available in struct irq_domain. Read it there instead.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/linuxppc-dev/878d7651-433a-46fe-a28b-1b7e893fcbe0@linux.ibm.com/
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20251010120307.3281720-1-namcao@linutronix.de

Author: covanam

arch/powerpc/platforms/pseries/msi.c

@@ -443,8 +443,7 @@ static int pseries_msi_ops_prepare(struct irq_domain *domain, struct device *dev
  */
 static void pseries_msi_ops_teardown(struct irq_domain *domain, msi_alloc_info_t *arg)
 {
-	struct msi_desc *desc = arg->desc;
-	struct pci_dev *pdev = msi_desc_to_pci_dev(desc);
+	struct pci_dev *pdev = to_pci_dev(domain->dev);
 
 	rtas_disable_msi(pdev);
 }