pinctrl: berlin: fix the dt_free_map function

The berlin_pinctrl_dt_free_map function tries to free memory
allocated and handled by the of subsystem. This is wrong and
already handled by pinctrl_dt_free_maps() which calls
of_node_put().

This patch fixes the Berlin pinctrl way of freeing its maps,
avoiding a kernel BUG(), by using the common
pinctrl_utils_dt_free_map function instead.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>