pinctrl: st: st_pinconf_dbg_show wrong format string

function is defined as unsigned int.
So we need %u to print it.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>