iommu/arm-smmu: fix possible null-ptr-deref in arm_smmu_device_probe()

It will cause null-ptr-deref when using 'res', if platform_get_resource()
returns NULL, so move using 'res' after devm_ioremap_resource() that
will check it to avoid null-ptr-deref.
And use devm_platform_get_and_ioremap_resource() to simplify code.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220425114136.2649310-1-yangyingliang@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>