Bluetooth: controller: Fix nRF52840 Coded PHY timings

Fix the nRF52840 Coded PHY radio timings based on testing
with conformance tester.

Fixes the following conformance tests:
LL/CON/MAS/BV-52-C [Master Receiving Data, LE Coded, CI Change]
LL/CON/MAS/BV-54-C [Slave Receiving Data, LE Coded, CI Change]

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>