freescale/imx6-sabresd: lock down kernel headers to the kernel version

freescale/imx6-sabresd: lock down kernel headers to the kernel version

The current defconfigs for iMX6 SABRESD kernel 3.10.17 from the Freescale
git repository. This kernel is older than the toolchain kernel headers
used in Buildroot (currently 3.16.3).

Explicitly lock down the kernel headers to match the version of the kernel
that is built.

Signed-off-by: Luca Ceresoli <[email protected]>
Tested-by: Vincent Stehlé <[email protected]>
Cc: Gilles Talis <[email protected]>
Cc: Gary Bisson <[email protected]>
Cc: Thomas Petazzoni <[email protected]>
Signed-off-by: Thomas Petazzoni <[email protected]>