platform_get_resource() may fail and return NULL, so we had better
check its return value to avoid a NULL pointer dereference a bit later
in the code. Fix it to use devm_platform_ioremap_resource_byname()
instead of calling platform_get_resource_byname() and devm_ioremap().

Link: https://lore.kernel.org/r/20200429015027.134485-1-weiyongjun1@huawei.comSigned-off-by: Wei Yongjun <weiyongjun1@huawei.com>
[lorenzo.pieralisi@arm.com: commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>