iommu: re-use local fwnode variable in iommu_ops_from_fwnode()

iommu_ops_from_fwnode() stores &iommu_spec->np->fwnode in local
variable, so use it to simplify the code (iommu_spec is not changed
between these dereferences).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240216144027.185959-4-krzysztof.kozlowski@linaro.org


Signed-off-by: Joerg Roedel <jroedel@suse.de>