expat: fix CVE-2024-45491

An issue was discovered in libexpat before 2.6.3. dtdCopy in xmlparse.c can have an
integer overflow for nDefaultAtts on 32-bit platforms (where UINT_MAX equals SIZE_MAX).

(From OE-Core rev: fb5ca8b9dcb00ff579ee70295b68aecdb3084b38)

Signed-off-by: Archana Polampalli <archana.polampalli@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>