libctf: avoid mingw warning

A missing paren led to an intended cast to avoid dependence on the size
of size_t in one argument of ctf_err_warn applying to the wrong type by
mistake.

libctf/ChangeLog:

	* ctf-serialize.c (ctf_write_mem): Fix cast.

libctf/ctf-serialize.c

@@ -1319,7 +1319,7 @@ ctf_write_mem (ctf_dict_t *fp, size_t *size, size_t threshold)
 	{
 	  ctf_set_errno (fp, ENOMEM);
 	  ctf_err_warn (fp, 0, 0, _("ctf_write_mem: cannot allocate %li bytes"),
-			(unsigned long) fp->ctf_size + sizeof (struct ctf_header));
+			(unsigned long) (fp->ctf_size + sizeof (struct ctf_header)));
 	  return NULL;
 	}
       ctf_flip_header (hp);