iommu: Replace iommu_group_device_count() with list_count_nodes()

No reason to wrapper a standard function, just call the library directly.
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/1-v5-1b99ae392328+44574-iommu_err_unwind_jgg@nvidia.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -1125,17 +1125,6 @@ void iommu_group_remove_device(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(iommu_group_remove_device);
 
-static int iommu_group_device_count(struct iommu_group *group)
-{
-	struct group_device *entry;
-	int ret = 0;
-
-	list_for_each_entry(entry, &group->devices, list)
-		ret++;
-
-	return ret;
-}
-
 static int __iommu_group_for_each_dev(struct iommu_group *group, void *data,
 				      int (*fn)(struct device *, void *))
 {
@@ -2083,7 +2072,7 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
 	 */
 	mutex_lock(&group->mutex);
 	ret = -EINVAL;
-	if (iommu_group_device_count(group) != 1)
+	if (list_count_nodes(&group->devices) != 1)
 		goto out_unlock;
 
 	ret = __iommu_attach_group(domain, group);
@@ -2114,7 +2103,7 @@ void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
 
 	mutex_lock(&group->mutex);
 	if (WARN_ON(domain != group->domain) ||
-	    WARN_ON(iommu_group_device_count(group) != 1))
+	    WARN_ON(list_count_nodes(&group->devices) != 1))
 		goto out_unlock;
 	__iommu_group_set_core_domain(group);