fix the issue widget id can be wrong after restore

Bug: 171774227
Test: manual testing
1. randomly add/remove widgets to workspace
2. create a backup (Settings > System > Backup)
3. reset the device
4. restore from the backup
5. verify all of the widgets are restored properly

Change-Id: Id65e474dd9349aca715d7e6b88f8d58bc63066ae