iommu: Move more initialization to __iommu_probe_device()

Move the calls to dev_iommu_get() and try_module_get() into
__iommu_probe_device(), so that the callers don't have to do it on
their own.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20200429133712.31431-34-joro@8bytes.org


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