saft: Write the modified firmware body to flashrom after updating ecbin

The original code has an issue that we don't write the firwmare body back
to the system via flashrom. So any change doesn't take effect. This CL
fixes this issue.

BUG=chrome-os-partner:12997
TEST=After merging some EC update test changes, run:
run_remote_test.sh -a "new_ec=ec_autest_image.bin" firmware_UpdateECBin/control$

Change-Id: I40c83f5bd2c4774e02341ac21f4b6167e713638f
Reviewed-on: https://gerrit.chromium.org/gerrit/31705
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
1 file changed