memory: samsung: exynos5422-dmc: Convert to devm_platform_ioremap_resource

Use devm_platform_ioremap_resource() to simplify code.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Acked-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>