tools/power turbostat: Fix Bzy_MHz documentation typo

The code calculates Bzy_MHz by multiplying TSC_delta * APERF_delta/MPERF_delta
The man page erroneously showed that TSC_delta was divided.

Signed-off-by: Peng Liu <liupeng17@lenovo.com>
Signed-off-by: Len Brown <len.brown@intel.com>