The iommu_paging_domain_alloc() function doesn't return NULL pointers,
it returns error pointers. Update the check to match.
Fixes: 45c690aea8 ("drm/tegra: Use iommu_paging_domain_alloc()")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ba31cf3a-af3d-4ff1-87a8-f05aaf8c780b@stanley.mountain
a85df8c7b5