Callees always return 0, except for FreeBSD's cdrom_eject(), which
returns -ENOTSUP when the device is in a terminally wedged state.

The only caller is bdrv_eject(), and it maps -ENOTSUP to 0 since
commit 4be9762a.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>