Update ext2fs interface usage for group descriptor
Update ext2fs interface usage for group descriptor

The current e2fsprogs-libs changes the group descriptor access method,
requiring an additional function call now.

BUG=chromium-os:22172
TEST=lumpy64 build & boot
CQ-DEPEND=I70114b582b46c26b69ab822b8c33b32f03ef9db0

Change-Id: I98c6bab1a7f7af8a7c351ce04cebf07813c3a1ab
Signed-off-by: Kees Cook <50cb10d2be062154b17ab4d66a4eab34f1cf1c84@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/15994

marineam/update_engine,marineam/update_engine,mjg59/update_engine,mjg59/update_engine,endocode/update_engine,endocode/update_engine,endocode/update_engine,marineam/update_engine,mjg59/update_engine,marineam/update_engine