It was reported to me on IRC today, that my change causes issues with
kernel versions between 4.14 and 4.19.
It's because I've wrongly used `git describe` in order to get kernel
version where we should disable noisy DTC checks, but I should've used
`git tag --contains` instead.
Fixes: cbbef976e2 ("build: dtc: Disable noisy warnings by default")
Signed-off-by: Petr Štetiar <ynezz@true.cz>