bus: uniphier-system-bus: use devm_platform_ioremap_resource()

Replace the chain of platform_get_resource() and devm_ioremap_resource()
with devm_platform_ioremap_resource().

This allows to remove the local variable for (struct resource *), and
have one function call less.

Link: https://lore.kernel.org/r/20190905032122.26076-1-yamada.masahiro@socionext.com


Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>