PCI: Simplify pci_pio_to_address()

Simplify pci_pio_to_address() by removing an unnecessary local variable.
No functional change intended.

Link: https://lore.kernel.org/r/20230824193712.542167-8-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>