Add a type cast for set8->pairs to fix below compile warning:

main.c: In function 'sets_patch':
main.c:699:50: warning: comparison of distinct pointer types lacks a cast
  699 |        BUILD_BUG_ON(set8->pairs != &set8->pairs[0].id);
      |                                 ^~

Fixes: 9707ac4f ("tools/resolve_btfids: Refactor set sorting with types from btf_ids.h")
Signed-off-by: Liwei Song <liwei.song.lsong@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20240722083305.4009723-1-liwei.song.lsong@gmail.com