[IA64] Bugfix for system with 32 cpus

On a system where there are no hot pluggable cpus "additional_cpus"
is still set to -1 at the point where we call per_cpu_scan_finalize().
If we didn't find an SRAT table and so pick the default "32" for the
number of cpus, when we get to:
high_cpu = min(high_cpu + reserve_cpus, NR_CPUS);
we will end up initializing for just 31 cpus ... and so we will
die horribly when bringing up cpu#32.

Problem introduced by: 2c6e6db4
"Minimize per_cpu reservations."

Acked-by: Robin Holt <holt@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>