Bluetooth: Controller: Fix missing window widening in ull_periph_setup

No window widening was applied to conn_offset_us causing the initial
ticker_cb to get called slightly too late

Apply window_widening_periodic_us to conn_offset_us, since this is the
worst-case window widening (win_offset is not allowed to be larger than
a connection interval) and is applied in the LLL window size already

Fixes EBQ failure in LL/TIM/PER/BV-02-C

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