Bluetooth: Controller: Fix b2b rx shorts

This fixes Radio Rx when switching back-to-back is
used and device support CTE. For the CTE reception we need to use
PHYEND->DISABLE short instead of END->DISABLE short.
Using NRF_RADIO_SHORTS_PDU_END_DISABLE short handles
both cases.

Signed-off-by: Kamil Gawor <Kamil.Gawor@nordicsemi.no>