iommu/exynos: Clean up bus_set_iommu()

Stop calling bus_set_iommu() since it's now unnecessary, and simplify
the init failure path accordingly.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/d7477ef546479300217ca7bccb44da8b02715a07.1660572783.git.robin.murphy@arm.com


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