cpufreq: schedutil: Remove update_lock comment from struct sugov_policy definition

Currently, update_lock is also used in sugov_update_single_freq().

The comment is not helpful anymore.

Signed-off-by: Yue Hu <huyue2@yulong.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
[ rjw: Subject edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>