linux: fix dtc compile with OpenBSD host

mk/kernel-vars.mk

@@ -25,7 +25,7 @@ endif
 # non-Linux platforms need elf.h
 ifneq ($(OS_FOR_BUILD),Linux)
 KERNEL_MAKE_OPTS+=	HOSTCFLAGS='$(HOST_CPPFLAGS) ${HOST_CFLAGS}'
-KERNEL_MAKE_OPTS+=	HOST_EXTRACFLAGS='-I${LINUX_DIR}/tools/include -I${LINUX_DIR}/usr/include -I${LINUX_DIR}/security/selinux/include -I${ADK_TOPDIR}/adk/include -DKBUILD_NO_NLS'
+KERNEL_MAKE_OPTS+=	HOST_EXTRACFLAGS='-I${LINUX_DIR}/tools/include -I${LINUX_DIR}/usr/include -I${LINUX_DIR}/security/selinux/include -I${ADK_TOPDIR}/adk/include -I${LINUX_DIR}/scripts/dtc/libfdt -DKBUILD_NO_NLS'
 else
 KERNEL_MAKE_OPTS+=	HOSTCFLAGS='${HOST_CFLAGS}'
 endif