devm_ioremap_resource() fails gracefully when given a NULL resource
pointer, so we don't need to check separately for failure from
platform_get_resource_byname().  Remove the redundant check.

[bhelgaas: changelog]
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>