cpufreq: governor: Drop gov_cancel_work()

There's no reason for gov_cancel_work() to exist at all, as it only
has one caller and the only thing done by that caller is to invoke
gov_cancel_work().

Accordingly, drop gov_cancel_work() and move its contents to the
caller.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>