drm/tegra: Check for NULL pointer instead of IS_ERR()
drm/tegra: Check for NULL pointer instead of IS_ERR()

iommu_domain_alloc() returns NULL on error, it never returns error
pointers.

Signed-off-by: Dan Carpenter <ff341aa343d564f9e53e9dcb6996be8c04859a66@oracle.com>
Signed-off-by: Thierry Reding <3055038c414aef68bf32c33b8118623e7554e0f2@nvidia.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs