fix comments

pkg/cloudprovider/providers/azure/azure_managedDiskController.go

@@ -193,10 +193,11 @@ func (c *ManagedDiskController) ResizeDisk(diskURI string, oldSize resource.Quan
 
 // get resource group name from a managed disk URI, e.g. return {group-name} according to
 // /subscriptions/{sub-id}/resourcegroups/{group-name}/providers/microsoft.compute/disks/{disk-id}
+// according to https://docs.microsoft.com/en-us/rest/api/compute/disks/get
 func getResourceGroupFromDiskURI(diskURI string) (string, error) {
 	fields := strings.Split(diskURI, "/")
-	if len(fields) != 9 {
-		return "", fmt.Errorf("disk URI(%s) is not expected", diskURI)
+	if len(fields) != 9 || fields[3] != "resourceGroups" {
+		return "", fmt.Errorf("invalid disk URI: %s", diskURI)
 	}
 	return fields[4], nil
 }