ACPI: build fix for u8 cpu_index

Local apic entries are only 8 bits, but it seemed to not be caught with u8
return value result in the check

cpu_index >= NR_CPUS becomming always false.

drivers/acpi/processor_core.c: In function `acpi_processor_get_info':
drivers/acpi/processor_core.c:483: warning: comparison is always false due to limited range of data type

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Kenji Kaneshige <kaneshige.kenji@soft.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>