bus: mvebu-mbus: Fix incorrect size for PCI aperture resources

reg[0] is the DT base, reg[1] is the DT length in bytes,
struct resource.end is the inclusive end address, so a -1 is required.

Tested on kirkwood.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>