util/cbfstool: Fix truncate command error handling and cbfs_image_from_buffer()

Check return value of cbfs_truncate_space() in cbfs_truncate().
Remove return from cbfs_image_from_buffer() to inform about invalid
image region when incorrect offset header was provided.
Also change header offset provided to mentioned function in
cbfs_expand_to_region() and cbfs_truncate_space() from zero
to HEADER_OFFSET_UNKNOWN, as they do not support images with cbfs master
header.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: Ib009212692fb3594a826436df765860f54837154
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66334
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

util/cbfstool/cbfs_image.h

@@ -6,6 +6,9 @@
 #include "common.h"
 #include "cbfs.h"
 
+
+#define HEADER_OFFSET_UNKNOWN (~0u)
+
 /* CBFS image processing */
 
 struct cbfs_image {