x86/PCI: Use struct_size() in pirq_convert_irt_table()

Use struct_size() instead of hand-writing it. It is less verbose, more
robust and more informative.

Link: https://lore.kernel.org/r/00a5cc2cd322e7dea26579916ac6dda9c637aa57.1684518118.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: tititiou36

arch/x86/pci/irq.c

@@ -136,14 +136,14 @@ static inline struct irq_routing_table *pirq_convert_irt_table(u8 *addr,
 	if (ir->signature != IRT_SIGNATURE || !ir->used || ir->size < ir->used)
 		return NULL;
 
-	size = sizeof(*ir) + ir->used * sizeof(ir->slots[0]);
+	size = struct_size(ir, slots, ir->used);
 	if (size > limit - addr)
 		return NULL;
 
 	DBG(KERN_DEBUG "PCI: $IRT Interrupt Routing Table found at 0x%lx\n",
 	    __pa(ir));
 
-	size = sizeof(*rt) + ir->used * sizeof(rt->slots[0]);
+	size = struct_size(rt, slots, ir->used);
 	rt = kzalloc(size, GFP_KERNEL);
 	if (!rt)
 		return NULL;