ACPI / PCI: pci_slot: replace printk(KERN_xxx) with pr_xxx()

Trivial changes to replace printk(KERN_xxx) with pr_xxx().

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>