Commit e4ab08be ("powerpc/isa-bridge: Remove open coded "ranges"
parsing") broke PASemi Nemo board booting. The issue is the ISA I/O
range was not getting mapped as the logic to handle no "ranges" was
inverted. If phb_io_base_phys is non-zero, then the ISA range defaults
to the first 64K of the PCI I/O space. phb_io_base_phys should only be 0
when looking for a non-PCI ISA region.

Fixes: e4ab08be ("powerpc/isa-bridge: Remove open coded "ranges" parsing")
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Link: https://lore.kernel.org/all/301595ad-0edf-2113-b55f-f5b8051ed24c@xenosoft.de/Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230505171816.3175865-1-robh@kernel.org