iommu: Use right function to get group for device

The iommu_group_get_for_dev() will allocate a group for a
device if it isn't in any group. This isn't the use case
in iommu_request_dm_for_dev(). Let's use iommu_group_get()
instead.

Fixes: d290f1e7 ("iommu: Introduce iommu_request_dm_for_dev()")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -1915,9 +1915,9 @@ int iommu_request_dm_for_dev(struct device *dev)
 	int ret;
 
 	/* Device must already be in a group before calling this function */
-	group = iommu_group_get_for_dev(dev);
-	if (IS_ERR(group))
-		return PTR_ERR(group);
+	group = iommu_group_get(dev);
+	if (!group)
+		return -EINVAL;
 
 	mutex_lock(&group->mutex);