ide-tape: change IDE_AFLAG_IGNORE_DSC non-atomically

There are two sites where the flag is being changed: ide_retry_pc
and idetape_do_request. Both codepaths are protected by hwif->busy
(ide_lock_port) and therefore we shouldn't need the atomic accesses.

Spotted-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>