util: Dereference the correct field

Fixes the following warning:

rarian-reg-full.c: In function ‘rrn_reg_parse_file_full’:
rarian-reg-full.c:144:55: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘RrnListEntry *’ {aka ‘struct _RrnListEntry *’} [-Wformat=]
  144 |             fprintf(stderr, "Error: Orphaned section %s not added.\n",
      |                                                      ~^
      |                                                       |
      |                                                       char *
  145 |                     sect->name);
      |                     ~~~~~~~~~~
      |                         |
      |                         RrnListEntry * {aka struct _RrnListEntry *}