tools/power/x86/intel-speed-select: Warn for invalid package id

When CPU is offline, we can't get package id. So print error for this
and don't use output.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>