pinctrl: oxnas: Rename pinctrl_utils_dt_free_map to pinctrl_utils_free_map

Rename pinctrl_utils_dt_free_map to pinctrl_utils_free_map, introduced in
d32f7fd3 ("pinctrl: Rename pinctrl_utils_dt_free_map to pinctrl_utils_free_map")
but not reported into oxnas driver.

Fixes: 611dac1e ("pinctrl: Add Oxford Semiconductor OXNAS pinctrl and gpio driver")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>