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

commit 4d2b496f19f3c2cfaca1e8fa0710688b5ff3811d upstream.

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

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>