ACPI: acpi_pad: simplify code to avoid false gcc build warning

acpi_pad.c:432: warning: ‘num_cpus’ may be used uninitialized in this function

gcc 4.4.4 was unable to notice that num_cpus is always set.
Re-arrange the code to un-confuse gcc, and also make
it easier for humans to read....

Signed-off-by: Len Brown <len.browns@intel.com>