eclass/cros-kernel2: use ${SYSROOT} not ${ROOT}

${SYSROOT} is more correct:
 * ${ROOT} is for pkg_* phases (e.g., post-build installation to a live
   filesystem)
 * ${SYSROOT} is for build-time phases, like src_configure()

${SYSROOT} was a CrOS extension, now standardized in EAPI 7.

Revbump accomplished via:

  sed -i '/coolest prime/s:107:109:' sys-kernel/chromeos*/*9999.ebuild

BUG=none
TEST=kernel build

Change-Id: Ib3bb64223140c95353ffd705aa1b62928dad050d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2001093
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Commit-Queue: Brian Norris <briannorris@chromium.org>
11 files changed