fix calloc warning

The following warning occurs with gcc-14.2.0

../src/libaacs/unit_key.c: In function '_assign_titles': ../src/libaacs/unit_key.c:123:40: warning: 'calloc' sizes specified with 'sizeof' in the earlier argument and not in the later argument [-Wcalloc-transposed-args] 123 | uk->title_cps_unit = calloc(sizeof(uint16_t), num_titles + 2); | ^~~~~~~~ ../src/libaacs/unit_key.c:123:40: note: earlier argument should specify number of elements, later size of each element