tools/power x86_energy_perf_policy: Fix file leak in get_pkg_num()

In function get_pkg_num() if fopen_or_die() succeeds it returns a file
pointer to be used. But fclose() is never called before returning from
the function.

Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>