pinctrl: aspeed: Wrap -Woverride-init with cc-option

Clang does not support this option:

warning: unknown warning option '-Woverride-init'; did you mean
'-Woverride-module'? [-Wunknown-warning-option]
1 warning generated.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>