update grain name for ceph OSDs

Related-Prod: PROD-35230
Change-Id: Idbd3114d0d6e1d802a2a925dbc5a83136fd2a5f4
diff --git a/ceph-backend-migration.groovy b/ceph-backend-migration.groovy
index a9bf720..22809c8 100644
--- a/ceph-backend-migration.groovy
+++ b/ceph-backend-migration.groovy
@@ -91,7 +91,7 @@
             }
 
             def target_hosts = salt.getMinions(pepperEnv, TARGET)
-            def device_grain_name =  salt.getPillar(pepperEnv,"I@ceph:osd","ceph:osd:lvm_enabled")['return'].first().containsValue(true) ? "ceph_volume" : "ceph_disk"
+            def device_grain_name =  "ceph_disk"
             for (tgt in target_hosts) {
                 def osd_ids = []