[Buildroot] [PATCH] configs:nitrogen{6sx, 6x, 7, 8m}: fix typo in kernel headers version

[Gary Bisson]

Hi Romain,

On Sat, Feb 29, 2020 at 11:45:46PM +0100, Romain Naour wrote:
> A typo has been introduced during the last version bump [1].

Oops, bad sed command on my end :(

Thanks for the patch!
Gary