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 <bhelgaas@google.com>

drivers/pci/bus.c

@@ -202,6 +202,9 @@ void pci_bus_add_devices(const struct pci_bus *bus)
 		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) {