pinctrl: at91-pio4: fix "Prefer 'unsigned int' to bare use of 'unsigned'"

Fix "Prefer 'unsigned int' to bare use of 'unsigned'" checkpatch.pl
warning.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Link: https://lore.kernel.org/r/1611747945-29960-4-git-send-email-claudiu.beznea@microchip.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>