scsi_id: use _cleanup_free_ on buffer allocated by get_file_options

scsi_id: use _cleanup_free_ on buffer allocated by get_file_options

This simplifies the code a bit and hopefully fixes Coverity finding
CID 1382966. There was not actually a resource leak here (Coverity
seemed to be confused by thinking log_oom() could actually return 0),
but the fix doesn't hurt and should make this code more resilient to
future refactorings.

Tested: builds fine, manually called scsi_id, seems to work ok.