pinctrl/mediatek: fix spelling mistake in dev_err error message

Trivial change, fix spelling mistake 'invaild' -> 'invalid' in
dev_err message.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>