arm64: dts: juno: Correct PCI IO window

The PCIe root complex on Juno translates the MMIO mapped
at 0x5f800000 to the PIO address range starting at 0
(which is common because PIO addresses are generally < 64k).
Correct the DT to reflect this.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>