pinctrl: abx500: fix build warning

pinctrl-abx500.c: In function 'abx500_gpio_dbg_show_one':
pinctrl-abx500.c:534:14: warning: 'pud' may be used
uninitialized in this function [-Wuninitialized]

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