CTF: incorrect underlying type setting for enumeration types

CTF: incorrect underlying type setting for enumeration types

A bug was filed against the incorrect underlying type setting for
an enumeration type, which was caused by a copy and paste error.
This patch fixes the problem by setting it by calling objfile_int_type,
which was originally dwarf2_per_objfile::int_type, with ctf_type_size bits.
Also add error checking on ctf_func_type_info call.