FROMLIST: iommu/of: Take a ref to the IOMMU driver during ->of_xlate()

Ensure that we hold a reference to the IOMMU driver module while calling
the '->of_xlate()' callback during early device probing.

Signed-off-by: Will Deacon <will@kernel.org>
Bug: 140290589
Link: https://lore.kernel.org/lkml/20191121114918.2293-6-will@kernel.org/


Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: Ica9ef2d5ed172c2451c0a19538dc28852c2270d5