swcore: multiport LL, fix write ports split

modules/wrsw_swcore/swc_multiport_linked_list.vhd

@@ -131,7 +131,7 @@ architecture syn of swc_multiport_linked_list is
     variable nidx : integer range 0 to g_num_ports;
   begin
     if idx_h > g_num_ports-1 then
-      nidx := g_num_ports;
+      nidx := g_num_ports-1;
     else
       nidx := idx_h;
     end if;