configs: beagleboardx15: fixate the header series
The kernel headers version used to be default when the default was
still 4.9. Now, however, we switched the default headers version to
4.10 but the beagleboardx15 kernel is still 4.9, so we have to set
the kernel headers version explicitly.
Fixes https://gitlab.com/buildroot.org/buildroot/builds/11700987
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Arnout Vandecappelle