gpio: amd-fch: Fix type error found by sparse

Sparse complains:

gpio-amd-fch.c:45:27: sparse: expected void *
gpio-amd-fch.c:45:27: sparse: got void [noderef] <asn:2> *
gpio-amd-fch.c:45:27: sparse: warning: incorrect type in return
		              expression (different address spaces)
gpio-amd-fch.c:56:9: sparse:  expected void const volatile [noderef]
		              <asn:2> *addr
gpio-amd-fch.c:56:9: sparse:  expected void volatile [noderef] <asn:2> *addr
gpio-amd-fch.c:56:9: sparse:  got void *ptr
gpio-amd-fch.c:56:9: sparse:  warning: incorrect type in argument 1 (different address spaces)

I think it is because void * is returned rather than void __iomem *,
so fix it up.

Cc: Enrico Weigelt <info@metux.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>