parisc: fix kernel BUG at arch/parisc/include/asm/mmzone.h:50 (part 2)

Make sure that we really return -1 (instead of 0x00ff) as node id for
page frame numbers which are not physically available.

This finally fixes the kernel panic when running
cat /proc/kpageflags /proc/kpagecount.

Theoretically this patch now limits the number of physical memory ranges
to 127 instead of 254, but currently we have MAX_PHYSMEM_RANGES
hardcoded to 8 which is sufficient for all existing parisc machines.

Signed-off-by: Helge Deller <deller@gmx.de>