configs/chromebook_elm_defconfig: use linux headers same as kernel (5.9 series)
Use linux headers same as kernel (5.9 series).
Fixes:
- https://gitlab.com/buildroot.org/buildroot/-/jobs/917539050
Incorrect selection of kernel headers: expected 5.10.x, got 5.9.x
Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>