Bluetooth: Controller: Use event_offset = 2 for large CIG Sync Delays

For a CIG with a CIG Sync Delay larger than a SDU interval, we cannot
be sure that we can target the very next ISO event when the CIG event
is ongoing; Only reduce event_offset if CIG Sync Delay is smaller
than an SDU interval

Signed-off-by: Troels Nilsson <trnn@demant.com>