bluetooth: controller: nRF52811: fix LE Coded S2 Radio Timings

The nRF52811 Radio is similar to nRF52840 and exhibits
similar Radio Timings constants. We align the LE Coded
PHY (S2) RX chain delay with that of nRF52840, which,
eventually fixes the TIFS for nRF52811. In nRF52840 we
correct the inline comment only.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>