pinctrl: at91-pio4: fix memleak after using dt map

configs is allocated by pinconf_generic_parse_dt_config(),
pinctrl_utils_add_map_configs() duplicates configs so it can and has to
be freed to prevent memory leaks.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Reported-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>