At present this uses a true return to indicate it found a file. Adjust it
to use 0 for this, so it is consistent with other functions.
Update its callers accordingly and add a check for malloc() failure in
file_cbfs_fill_cache().
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
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