Cleanup nr_slot_fep_ul

Rename nr_slot_fep_ul to nr_symbol_fep_ul to relfect its function

Simplify logic so that the function does not require RU context and
the implementation is not dependent on the implementation of RU buffer management.

This makes the function easier to understand and moves the responsibility
to set the correct buffer offset on the caller.

openair1/SIMULATION/NR_PHY/prachsim.c

@@ -758,7 +758,12 @@ int main(int argc, char **argv){
 
         for (l = 0; l < frame_parms->symbols_per_slot; l++) {
           for (aa = 0; aa < frame_parms->nb_antennas_rx; aa++) {
-            nr_slot_fep_ul(frame_parms, ru->common.rxdata[aa], ru->common.rxdataF[aa], l, slot, ru->N_TA_offset);
+            nr_symbol_fep_ul(frame_parms,
+                             (c16_t *)ru->common.rxdata[aa],
+                             (c16_t *)&ru->common.rxdataF[aa][frame_parms->ofdm_symbol_size * l],
+                             l,
+                             slot,
+                             ru->N_TA_offset);
           }
         }