tools/power turbostat: Survive sparse die_id

Turbostat assumed that every package had a die_id = 0.
When this assumption was violated, it exited
when looking for the package uncore frequency:

turbostat: /sys/.../intel_uncore_frequency/package_01_die_00/current_freq_khz: open failed: No such file or directory

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