pb-2867: fix restore path issue for CSI backups
pb-2867: fix restore path issue for CSI backups

- fix the variable scope related issue in the restore logic of CSI backup.
- changed the switch case to have right type assertion check

Signed-off-by: Lalatendu Das <298fa1936b82486d6ca337c54cac35f903c3b12d@purestorage.com>

libopenstorage/stork,libopenstorage/stork,libopenstorage/stork