tools/power/x86/intel_pstate_tracer: Fix non root execution for post processing a trace file

This script is supposed to be allowed to run with regular user
privileges if a previously captured trace is being post processed.

Commit fbe31388 (tools/power/x86/intel_pstate_tracer: Free the
trace buffer memory) introduced a bug that breaks that option.

Commit 35459105 (tools/power/x86/intel_pstate_tracer: Add
optional setting of trace buffer memory allocation) moved the code
but kept the bug.

This patch fixes the issue.

Fixes: 35459105 (tools/power/x86/intel_pstate_tracer: Add optional ...)
Signed-off-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>