net: gemini: Use devm_platform_get_and_ioremap_resource()

Use devm_platform_get_and_ioremap_resource() to simplify
code.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>