pinctrl: update document for pinconf_generic_parse_dt_config

The returned configs from pinconf_generic_parse_dt_config() is
duplicated from original. Make it clear it must be freed when no
longer necessary.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinconf-generic.c

@@ -220,6 +220,7 @@ static void parse_dt_cfg(struct device_node *np,
  * parse the config properties into generic pinconfig values.
  * @np: node containing the pinconfig properties
  * @configs: array with nconfigs entries containing the generic pinconf values
+ *           must be freed when no longer necessary.
  * @nconfigs: umber of configurations
  */
 int pinconf_generic_parse_dt_config(struct device_node *np,