PCI: designware: Remove incorrect io_base assignment

"pp->io" is an I/O resource, e.g., "[io 0x0000-0xffff]"; "pp->io_base" is
the CPU physical address of a region where the host bridge converts CPU
memory accesses into PCI I/O transactions.

Corrupting pp->io_base by assigning pp->io->start to it breaks access to
the PCI I/O space, as reported by Kishon.

Remove the invalid assignment.

[bhelgaas: changelog]
Fixes: 0021d22b ("PCI: designware: Use of_pci_get_host_bridge_resources() to parse DT")
Reported-and-tested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>