iommu: Fix static checker warning in iommu_insert_device_resv_regions

In case the device reserved region list is void, the returned value
of iommu_insert_device_resv_regions is uninitialized. Let's return 0
in that case.

This fixes commit 6c65fb31 ("iommu: iommu_get_group_resv_regions").
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -205,7 +205,7 @@ iommu_insert_device_resv_regions(struct list_head *dev_resv_regions,
 				 struct list_head *group_resv_regions)
 {
 	struct iommu_resv_region *entry;
-	int ret;
+	int ret = 0;
 
 	list_for_each_entry(entry, dev_resv_regions, list) {
 		ret = iommu_insert_resv_region(entry, group_resv_regions);