tools/power/x86/intel_pstate_tracer: fix a broken y-axis scale

A fixed y-axis scale was missed during a change to autoscale.

Correct it.

Fixes: 709bd70d ("tools/power/x86/intel_pstate_tracer: change several graphs to autoscale y-axis")
Signed-off-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>