Bluetooth: controller: split: Fix NRF_CCM overrun

Fix missing assignment of NRF_CCM->MAXPACKETSIZE register
for PDU sizes smaller than 251 bytes. If there is CRC errors
causing PDU length fields to be higher than configured PDU
buffer sizes in the controller, without the MAXPACKETSIZE
register set to correct PDU size, CCM module could overrun
the PDU buffer and cause memory corruption. This fix is
applicable for all nRF52 Series SoCs except nRF52832 SoC.

Fixes #21107.

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