cros-coreboot: get vga settings from .config

If we copied the config file from $FILESDIR, then parsing the config
file from the source tree doesn't make sense.  Make sure we extract
the settings from the right file.

BUG=chromium:348403
TEST=modified $FILESDIR/config and saw changes reflected in output filename

Change-Id: I810a44918cb711041d5e38bc99a247c7402414ac
Reviewed-on: https://chromium-review.googlesource.com/296092
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Stefan Reinauer <reinauer@chromium.org>
1 file changed