pinctrl: aspeed: Fix missed include

Some SPDX churn made my fixes drop an important include
from the Aspeed pinctrl header. Fix it up.

Cc: Andrew Jeffery <andrew@aj.id.au>
Reported-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>