Fix device naming for loopback devices

Fixes: PROD-24386 (PROD:24386)

Change-Id: Id6e5d1f6e52d8dec1796610029b653f78a54a271
diff --git a/linux/storage/loopback.sls b/linux/storage/loopback.sls
index 883b02e..9511d0f 100644
--- a/linux/storage/loopback.sls
+++ b/linux/storage/loopback.sls
@@ -30,7 +30,7 @@
   - template: jinja
   - defaults:
     file: {{ loopback.file }}
-    device_name: "/dev/loop{{ loop.index0 }}"
+    device_name: "/dev/{{ device }}"
 
 setup-loopback-{{ device }}:
   service.running: