PCI: mvebu: Fix I/O space end address calculation

pcie->realio.end should be the address of last byte of the area,
therefore using resource_size() of another resource is not correct, we
must substract 1 to get the address of the last byte.

Fixes: 11be6547 ("PCI: mvebu: Adapt to the new device tree layout")
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>