Fix endless loop when trying to add a too large file to CBFS,

Fix endless loop when trying to add a too large file to CBFS,
and report the correct error code, and a hopefully helpful
error message.

Signed-off-by: Patrick Georgi <patrick.georgi@coresystems.de>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4692 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1