cpio: Fix wrong CRC with ASCII CRC for large files

Due to signedness, the checksum is not computed when filesize is bigger
a 2GB. Pick a fix for this problem from CPIO ML, where the fix has been
posted for 5 years. Since CPIO upstream is effectively unresponsive and
any and all attempts to communicate with the maintainer and get the fix
applied upstream failed, add the fix here instead.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>