PM / OPP: add documentation to RCU head in struct opp

commit dde8437 (PM / OPP: RCU reclaim) introduced rcu_head for
struct opp. This aids freeing using kfree_rcu. However, we missed
adding documentation for the same. This generates kernel doc warning:
Warning(drivers/base/power/opp.c:70): No description found for
parameter 'head'

Add documentation as appropriate.

[rjw: Changelog]
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index 32ee0fc7ea54..f0077cb8e249 100644
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -55,6 +55,7 @@
  * @rate:       Frequency in hertz
  * @u_volt:     Nominal voltage in microvolts corresponding to this OPP
  * @dev_opp:    points back to the device_opp struct this opp belongs to
+ * @head:       RCU callback head used for deferred freeing
  *
  * This structure stores the OPP information for a given device.
  */