iommu/qcom: Simplify a test in 'qcom_iommu_add_device()'

'iommu_group_get_for_dev()' never returns NULL, so this test can be
simplified a bit.

This way, the test is consistent with all other calls to
'iommu_group_get_for_dev()'.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/qcom_iommu.c

@@ -539,8 +539,8 @@ static int qcom_iommu_add_device(struct device *dev)
 	}
 
 	group = iommu_group_get_for_dev(dev);
-	if (IS_ERR_OR_NULL(group))
-		return PTR_ERR_OR_ZERO(group);
+	if (IS_ERR(group))
+		return PTR_ERR(group);
 
 	iommu_group_put(group);
 	iommu_device_link(&qcom_iommu->iommu, dev);