pinctrl: pinctrl-single.c: Cleaning up wrong format string usage

%d in format string used, but the type is unsigned int

This was found using a static code analysis program called cppcheck

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>