gpio: ixp4xx: Use devm_platform_ioremap_resource()

Convert platform_get_resource(),devm_ioremap_resource() to a single
call to devm_platform_ioremap_resource(), as this is exactly what this
function does.

Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>