cbfstool: Add way to access entire backing data for a buffer

This is required to handle certain relative-to-flash-start offsets.

BUG=none
BRANCH=tot
TEST=none

Change-Id: I8b30c7b532e330af5db4b8ed65b21774c6cbbd25
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 596ba1aaa62aedb2b214ca55444e3068b9cb1044
Original-Change-Id: Idc9a5279f16951befec4d84aab35117988f7edb7
Original-Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/312220
Original-Commit-Ready: Patrick Georgi <pgeorgi@chromium.org>
Original-Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/12415
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/util/cbfstool/common.c b/util/cbfstool/common.c
index 44836ab..09a7449 100644
--- a/util/cbfstool/common.c
+++ b/util/cbfstool/common.c
@@ -115,7 +115,7 @@
 		buffer->name = NULL;
 	}
 	if (buffer->data) {
-		free(buffer->data - buffer->offset);
+		free(buffer_get_original_backing(buffer));
 		buffer->data = NULL;
 	}
 	buffer->offset = 0;