iommu/tegra: smmu: remove sanity checks during dev notifications.

iommu/tegra: smmu: remove sanity checks during dev notifications.

arm_iommu_detach_device doesn't reset mapping to NULL.
remove sanity checks during device  notifications to avoid
incorrect warning messages.

Bug 1446597

Change-Id: I7a49cd9ba464a1007260260b5fe41113db0b7689
Signed-off-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/365172
(cherry picked from commit 246a182ef16776f9db88559b5b3c3d7b07ebd8cd)
Reviewed-on: http://git-master/r/375600
Reviewed-by: Bryan Wu <pengw@nvidia.com>
Tested-by: Bryan Wu <pengw@nvidia.com>
Reviewed-by: Eric Brower <ebrower@nvidia.com>
Reviewed-by: Matthew Pedro <mapedro@nvidia.com>