heimdal: Pass the correct pointer to free in an error case

[jhb]

Summary

This fixes a warning reported by GCC 14 on stable/14:

crypto/heimdal/lib/hdb/keys.c:241:13: warning: 'free' called on pointer 'ext' with nonzero offset 16 [-Wfree-nonheap-object]

241 |             free(hist_keys);
    |             ^~~~~~~~~~~~~~~

crypto/heimdal/lib/hdb/keys.c:234:15: note: returned from 'calloc'

234 |         ext = calloc(1, sizeof (*ext));
    |               ^~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 5000d023a446 ("heimdal-kadmin: Add support for the -f dump option")