drivers: gpio: amd-fch: make resource struct const

The struct resource field is statically initialized
and may never change. Therefore make it const.

Signed-off-by: Enrico Weigelt <info@metux.net>
Link: https://lore.kernel.org/r/1560787211-15443-1-git-send-email-info@metux.net


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