vboot: rename ReadFileString() to ReadFileFirstLine()

To make it clear, rename ReadFileString() to ReadFileFirstLine() as it
is designed for reading the first line of file.

BRANCH=none
BUG=b:291036452
TEST=Run crossystem

Change-Id: Ifbf60449155892c15fed287d9a82adeebf964672
Signed-off-by: Tzung-Bi Shih <tzungbi@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/4729270
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
3 files changed