iommu/tegra-smmu: Fix return value check in tegra_smmu_group_get()

In case of error, the function iommu_group_alloc() returns ERR_PTR() and
never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().

Fixes: 7f4c9176f760 ("iommu/tegra: Allow devices to be grouped")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/iommu/tegra-smmu.c

@@ -832,7 +832,7 @@ static struct iommu_group *tegra_smmu_group_get(struct tegra_smmu *smmu,
 	group->soc = soc;
 
 	group->group = iommu_group_alloc();
-	if (!group->group) {
+	if (IS_ERR(group->group)) {
 		devm_kfree(smmu->dev, group);
 		mutex_unlock(&smmu->lock);
 		return NULL;