thermal: cpu_cooling: Appease the kernel-doc deity

Describe the function parameter to fix the following warning with make
W=1:

linux.git/drivers/thermal/cpu_cooling.c:92: warning: Function parameter
or member 'qos_req' not described in 'cpufreq_cooling_device'
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/ddb09e9728533c274edae7ff3da515b3cf7ef231.1574242756.git.amit.kucheria@linaro.org

drivers/thermal/cpu_cooling.c

@@ -63,6 +63,7 @@ struct time_in_idle {
  * @policy: cpufreq policy.
  * @node: list_head to link all cpufreq_cooling_device together.
  * @idle_time: idle time stats
+ * @qos_req: PM QoS contraint to apply
  *
  * This structure is required for keeping information of each registered
  * cpufreq_cooling_device.