u-boot: Fix CVE-2022-30767

u-boot: Fix CVE-2022-30767

This patch mitigates the vulnerability identified via CVE-2019-14196.
The previous patch was bypassed/ineffective, and now the vulnerability
is identified via CVE-2022-30767. The patch removes the sanity check
introduced to mitigate CVE-2019-14196 since it's ineffective.
filefh3_length is changed to unsigned type integer, preventing negative
numbers from being used during comparison with positive values during
size sanity checks.

Signed-off-by: Carlos Dominguez <carlos.dominguez@windriver.com>
Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>