iotests/backup-discard-source: convert size variable to be int

Make variable reusable in code for checks. Don't care to change "512 *
1024" invocations as they will be dropped in the next commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20240620144402.65896-2-vsementsov@yandex-team.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
1 file changed