tools/power turbostat: Allow Zero return value for some RAPL registers

turbostat aborted with below messages on a dual-package system,

   turbostat: turbostat.c:3744: rapl_counter_accumulate: Assertion `dst->unit == src->unit' failed.
   Aborted

This is because
1. the MSR_DRAM_PERF_STATUS returns Zero for one package, and non-Zero
   for another package
2. probe_msr() treats Zero return value as a failure so this feature is
   enabled on one package, and disabled for another package.
3. turbostat aborts because the feature is invalid on some package

Unlike the RAPL energy counter registers, MSR_DRAM_PERF_STATUS can
return Zero value, and this should not be treated as a failure.

Fix the problem by allowing Zero return value for RAPL registers other
than the energy counters.

Fixes: 7c6fee25 ("tools/power turbostat: Check for non-zero value when MSR probing")
Reported-by: Artem Bityutskiy <artem.bityutskiy@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>