iommu/tegra: smmu: Nullify stale pointer

iommu/tegra: smmu: Nullify stale pointer

The map* in smmu_map_prop points to the dma_iommu_mapping
which was destroyed. It may be possible that a client which registers
to this swgroup will be using the stale pointer and not create one
new dma_iommu_mapping * if this pointer is not set NULL.
Fix it by setting it NULL just before domain is destroyed.

Bug 200031739

Change-Id: I05ac3456074d6bbfe11cbc766e47de257d0e0ae5
Signed-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Reviewed-on: http://git-master/r/552080
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Hiroshi Doyu <hdoyu@nvidia.com>