iommu/arm-smmu: Retire probe deferral workaround

This reverts commit 229e6ee4.

Now that the fundamental ordering issue between arm_smmu_get_by_fwnode()
and iommu_device_register() is resolved, the race condition for client
probe no longer exists either, so retire the specific workaround.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/4167c5dfa052d4c8bb780f0a30af63dcfc4ce6c1.1733406914.git.robin.murphy@arm.com


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