In Linux kernel commit 8377bd2b9ee1 ("kbuild: Rename HOST_LOADLIBES to
KBUILD_HOSTLDLIBS") HOST_LOADLIBES was renamed to KBUILD_HOSTLDLIBS.
This patch adapts the OpenWrt kernel build to this new variable. Without
this change the kernel host tools would not link against the libraries
found in the staging directory.

Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>