cbfstool: Propogate compression errors back to the caller.

When compression fails for whatever reason, the caller should know about it
rather than blindly assuming it worked correctly. That can prevent half
compressed data from ending up in the image.

This is currently happening for a segment of depthcharge which is triggering
a failure in LZMA. The size of the "compressed" data is never set and is
recorded as zero, and that segment effectively isn't loaded during boot.

Change-Id: Idbff01f5413d030bbf5382712780bbd0b9e83bc7
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/187364
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit be48f3e41eaf0eaf6686c61c439095fc56883cec)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6960
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>