iommu/ipmmu-vmsa: Fix return value check in ipmmu_find_group_dma()

In case of error, the function iommu_group_get() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.

Fixes: 3ae4729202 ("iommu/ipmmu-vmsa: Add new IOMMU_DOMAIN_DMA ops")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/iommu/ipmmu-vmsa.c

@@ -871,7 +871,7 @@ static struct iommu_group *ipmmu_find_group_dma(struct device *dev)
 	sibling = ipmmu_find_sibling_device(dev);
 	if (sibling)
 		group = iommu_group_get(sibling);
-	if (!sibling || IS_ERR(group))
+	if (!sibling || !group)
 		group = generic_device_group(dev);
 
 	return group;