PCI: Remove return values from pcie_port_platform_notify() and relatives

Now that pcie_port_acpi_setup() always returns 0, make it and its callers
void functions and stop checking the return values.

[bhelgaas: changelog]
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>