scsi: scsi_debug: Fix memory leak if LBP enabled and module is unloaded

map_storep was not being vfree()'d in the module_exit call.

Cc: <stable@vger.kernel.org>
Signed-off-by: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>