Handle division by 0 gracefully in average channel level calculation
- Replaced division by zero assert with a conditional calculation of 'z' (inverse of 'y').
- Added a log message if 'y' is zero to handle the special case
nb_re_pdsch is directly linked to nb_rb_pdsch, if the latter is 0 the former is also 0 with this commit, the average channel level will be set to 0 and the inconsistency will be handled in later in nr_ue_pdsch_procedures with a demodulation failure
other minor changes:
- Improved clarity by using NR_NB_SC_PER_RB instead of hard-coded value 12 in nb of RBs calculation
addressing one of the issues found in #783
Edited by Guido Casati