Pucch2 polar rx dynamic range fix

fixes the overflow issue in the PUCCH2 RX with 4+ RX antennas and 12+ bits (polar code format). The fix scales the polar decoding LLR computation according to the number of RX antennas. The issue was clear for 100 MHz 4 RX antennas. Even "nr_pucchsim -s -5 -q 8 -P 2 -b 12 -R 273 -z4 -n1000" doesn't converge to 0 BLER with increasing SNR. The issue didn't appear in CI because of the bandwidth and antenna count limitations.