hotfix: revert value of 'rb_table_index'

This reverts commit 7f24927c43.

With value 13 uplink TDD for a 10MHz configuration was not working.
UDP traffic sent with: "iperf -c XX -u -b10M" was crashing
the eNB.

openair2/LAYER2/MAC/eNB_scheduler_ulsch.c

@@ -885,7 +885,7 @@ abort();
               rb_table_index=UE_template->pre_allocated_rb_table_index_ul;
             } else {
 	      mcs=10;//cmin (10, openair_daq_vars.target_ue_ul_mcs);
-              rb_table_index=13; // for PHR
+              rb_table_index=5; // for PHR
 	    }
 
             UE_list->eNB_UE_stats[CC_id][UE_id].ulsch_mcs2=mcs;