cpufreq: intel_pstate: Fix missing return statement

Fix missing return statement when writing "off" to intel_pstate status
sysfs I/F.

Fixes: 55671ea3

 ("cpufreq: intel_pstate: Free memory only when turning off")
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>