ide-disk: use IDE_DFLAG_MEDIA_CHANGED

Set IDE_DFLAG_MEDIA_CHANGED in ide_gd_open() to signalize
ide_gd_media_changed() that that media has changed (instead
of relying on IDE_DFLAG_REMOVABLE).

There should be no functional changes caused by this patch.

Acked-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>