qcow2: use Z_OK instead of 0 for deflateInit2 return code check

Use appropriate macro, corresponding to deflateInit2 spec.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
1 file changed