fix(ntfsprogs/mkntfs): use after free

[safocl]

mkntfs.c:4689:43: warning: pointer ‘bs_674’ used after ‘free’ [-Wuse-after-free]
 4689 |                                         bs->clusters_per_mft_record);
      |                                         ~~^~~~~~~~~~~~~~~~~~~~~~~~~
mkntfs.c:4686:25: note: call to ‘free’ here
 4686 |                         free(bs);
      |                         ^~~~~~~~
mkntfs.c:4707:43: warning: pointer ‘bs_674’ used after ‘free’ [-Wuse-after-free]
 4707 |                                         bs->clusters_per_index_record);
      |                                         ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
mkntfs.c:4703:25: note: call to ‘free’ here
 4703 |                         free(bs);
      |                         ^~~~~~~~