fs: cbfs: Fix out of bound access during CBFS walking through

fs: cbfs: Fix out of bound access during CBFS walking through

The call to file_cbfs_fill_cache() is given with the parameter
'start' pointing to the offset by the CBFS base address, but
with the parameter 'size' that equals to the whole CBFS size.
During CBFS walking through, it checks files one by one and
after it pass over the end of the CBFS which is 4GiB boundary
it tries to check files from address 0 and so on, until the
overall size the codes checked hits to the given 'size'.

Fix this by passing 'start' pointing to the CBFS base address.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>