tools/power x86_energy_perf_policy: close /proc/stat in for_every_cpu()

Instead of returning out of for_every_cpu() we should break out of the loop=
 which will then tidy up correctly by closing the file /proc/stat.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Len Brown <len.brown@intel.com>