host/lib/flashrom: Free image data on flashrom_read_* failure BUG=b:431694612 TEST=make futil -j BRANCH=none Change-Id: I5f6e13294a9d1604edc99b14ac999374236060b2 Signed-off-by: Yu-Ping Wu <yupingso@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/6808998 Reviewed-by: Jakub "Kuba" Czapiga <czapiga@google.com>