include: always do unsigned left-shift in CTF_SET_STID

include: always do unsigned left-shift in CTF_SET_STID

This turns into a signed left shift by 31 bits, otherwise.  This is an
offset and is always treated as unsigned in any case, so add an
appropriate cast.

include/ChangeLog
2021-03-25  Nick Alcock  <nick.alcock@oracle.com>

	PR libctf/27628
	* ctf-api.h: Fix some indentation.
	(CTF_SET_STID): Always do an unsigned shift, even if STID is
	signed.