cpufreq: Remove unnecessary initialization of a local variable

Remove an unnecessary initializer for the 'ret' variable in
__cpufreq_set_policy().

[rjw: Modified the subject and changelog slightly.]
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>