PCI: Warn about failures instead of "must_check" functions

These places capture return values to avoid "must_check" warnings,
but we didn't *do* anything with the return values, which causes
"set but not used" warnings. We might as well do something instead
of just trying to evade the "must_check" warnings.

Signed-off-by: Bjorn Helgaas <[e-mail]>

drivers/pci/bus.c

···
 		if (dev->is_added)
 			continue;
 		retval = pci_bus_add_device(dev);
+		if (retval)
+			dev_err(&dev->dev, "Error adding device (%d)\n",
+				retval);
 	}
 
 	list_for_each_entry(dev, &bus->devices, bus_list) {

drivers/pci/setup-bus.c

···
 
 enable_all:
 	retval = pci_reenable_device(bridge);
+	if (retval)
+		dev_err(&bridge->dev, "Error reenabling bridge (%d)\n", retval);
 	pci_set_master(bridge);
 	pci_enable_bridges(parent);
 }

drivers/pci/slot.c

···
 {
 	struct hotplug_slot *slot = pci_slot->hotplug;
 	struct kobject *kobj = NULL;
-	int no_warn;
+	int ret;
 
 	if (!slot || !slot->ops)
 		return;
 	kobj = kset_find_obj(module_kset, slot->ops->mod_name);
 	if (!kobj)
 		return;
-	no_warn = sysfs_create_link(&pci_slot->kobj, kobj, "module");
+	ret = sysfs_create_link(&pci_slot->kobj, kobj, "module");
+	if (ret)
+		dev_err(&pci_slot->bus->dev, "Error creating sysfs link (%d)\n",
+			ret);
 	kobject_put(kobj);
 }
 EXPORT_SYMBOL_GPL(pci_hp_create_module_link);