freescale_imx6sxsabresd_defconfig: fix kernel headers version

Fixes https://travis-ci.org/buildroot/buildroot-defconfig-testing/jobs/123187910

Commit 1e5bc05a04d (configs: freescale_imx6*: bump version to
3.14.52-1.1.0_ga) updated the kernel but forgot to change the kernel headers
version to match.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/freescale_imx6sxsabresd_defconfig

@@ -5,8 +5,8 @@ BR2_cortex_a9=y
 # patches
 BR2_GLOBAL_PATCH_DIR="board/freescale/imx6sabre/patches"
 
-# Linux headers same as kernel, a 3.10 series
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_10=y
+# Linux headers same as kernel, a 3.14 series
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_14=y
 
 # system
 BR2_TARGET_GENERIC_GETTY_PORT="ttymxc0"