cpufreq: cpufreq_governor: Demote store_sampling_rate() header to standard comment block

There is no need for this to be denoted as kerneldoc.

Fixes the following W=1 kernel build warning(s):

 drivers/cpufreq/cpufreq_governor.c:46: warning: Function parameter or member 'attr_set' not described in 'store_sampling_rate'
 drivers/cpufreq/cpufreq_governor.c:46: warning: Function parameter or member 'buf' not described in 'store_sampling_rate'
 drivers/cpufreq/cpufreq_governor.c:46: warning: Function parameter or member 'count' not described in 'store_sampling_rate'

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