pinctrl: abx500: fix abx500_pin_config_set()

- Update abx500_pin_config_set() in order to take in
account PIN_CONFIG_BIAS_DISABLE state to disable
pull up or pull down.

- Rework error path.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>