[9fans] off by one in the pc kaddr

[Anthony Martin]

I've read through the MMU code more than
a few times and never noticed this.  Who
reads past tmpunmap anyways? ;)

  Anthony

diff -c /sys/src/9/pc/mmu.c /tmp/mmu.c
/sys/src/9/pc/mmu.c:934,940 - /tmp/mmu.c:934,940
  void*
  kaddr(ulong pa)
  {
-       if(pa > (ulong)-KZERO)
+       if(pa >= (ulong)-KZERO)
                panic("kaddr: pa=%#.8lux", pa);
        return (void*)(pa+KZERO);
  }