MIPS: OCTEON: use devm_platform_ioremap_resource

Note that error handling on the result of a call to platform_get_resource()
is unneeded when the value is passed to devm_ioremap_resource(), so remove
it. Then use the helper function that wraps the calls to
platform_get_resource() and devm_ioremap_resource() together.

Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>