mfd: wm831x-core: Supply description wm831x_reg_{un}lock args

Kerneldoc syntax is used, but not complete.  Descriptions required.

Prevents warnings like:

 drivers/mfd/wm831x-core.c:119: warning: Function parameter or member 'wm831x' not described in 'wm831x_reg_lock'
 drivers/mfd/wm831x-core.c:145: warning: Function parameter or member 'wm831x' not described in 'wm831x_reg_unlock'

Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: patches@opensource.cirrus.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/wm831x-core.c

@@ -114,6 +114,8 @@ static int wm831x_reg_locked(struct wm831x *wm831x, unsigned short reg)
  * The WM831x has a user key preventing writes to particularly
  * critical registers.  This function locks those registers,
  * allowing writes to them.
+ *
+ * @wm831x: pointer to local driver data structure
  */
 void wm831x_reg_lock(struct wm831x *wm831x)
 {
@@ -140,6 +142,8 @@ EXPORT_SYMBOL_GPL(wm831x_reg_lock);
  * The WM831x has a user key preventing writes to particularly
  * critical registers.  This function locks those registers,
  * preventing spurious writes.
+ *
+ * @wm831x: pointer to local driver data structure
  */
 int wm831x_reg_unlock(struct wm831x *wm831x)
 {