configs/orangepi_{lite2, one_plus}: use correct kernel headers version

In the following commits:

85f4bd94 configs/orangepi_lite2: fix kernel headers option
506cdeb2 configs/orangepi_one_plus: fix kernel headers option

We fixed the orangepi_lite2 and orangepi_one_plus defconfigs to use
the BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_X_Y option. However, we were
mistaken by the existing comment saying that 4.18 kernel headers
should be used. This was wrong, as the kernel source code in use is
4.19, so this commit fixes the
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_X_Y to use the correct version.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/165766089
  https://gitlab.com/buildroot.org/buildroot/-/jobs/165766093



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>