fs: cbfs: remove wrong header validation

fs: cbfs: remove wrong header validation

cbfs_fileheader.len indicates the content size of the file in the
cbfs, and it has nothing to do with cbfs_fileheader.offset which
is the starting address of the file in the cbfs.

Remove such check in file_cbfs_next_file(). Before this change
'cbfsinit' failed with 'Bad CBFS file'. After this change all cbfs
commands are working as expected.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
[bmeng: keep the necessary header sanity check]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>