libctf: fix ctf_archive_count return value on big-endian

libctf: fix ctf_archive_count return value on big-endian

This failed to properly byteswap its return value.

The ctf_archive format predates the idea of "just write natively and
flip on open", and byteswaps all over the place.  It's too easy to
forget one.  The next revision of the archive format (not versioned,
so we just tweak the magic number instead) should be native-endianned
like the dicts inside it are.

libctf/
	* ctf-archive.c (ctf_archive_count): Byteswap return value.