tools/power x86_energy_perf_policy: Fix "uninitialized variable" warnings at -O2

x86_energy_perf_policy first uses __get_cpuid() to check the maximum
CPUID level and exits if it is too low.  It then assumes that later
calls will succeed (which I think is architecturally guaranteed).  It
also assumes that CPUID works at all (which is not guaranteed on
x86_32).

If optimisations are enabled, gcc warns about potentially
uninitialized variables.  Fix this by adding an exit-on-error after
every call to __get_cpuid() instead of just checking the maximum
level.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Len Brown <len.brown@intel.com>