Check for failure of devm_ioremap_resource().

devm_ioremap_resource() validates the resource it receives, so if we check
for devm_ioremap_resource() failure, we need not check for failure of the
preceding platform_get_resource().

[bhelgaas: changelog]
Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>