PCI: Rename variables

In pci_bus_distribute_available_resources(), rename:

  io         =>  io_per_hp
  mmio       =>  mmio_per_hp
  mmio_pref  =>  mmio_pref_per_hp

No functional change; this is just to make a subsequent patch smaller.

[bhelgaas: extracted from https://lore.kernel.org/r/PSXP216MB0438587C47CBEDF365B1EA27803C0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM

]
Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>