boot-directdisk: Fix kernel location after STAGING_KERNEL_DIR change

This catches up with the STAGING_KERNEL_DIR location change
and uses the correct variable to future proof this issue.

[YOCTO #2783]

(From OE-Core rev: 28715eff6dff3415b1d7b0be8cbb465c417e307f)

(From OE-Core rev: f02a7341e37aec155772e1546d8b21ef2c9f5e9d)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/boot-directdisk.bbclass

@@ -46,7 +46,7 @@ build_boot_dd() {
 	IMAGE=${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.hdddirect
 
 	install -d ${HDDDIR}
-	install -m 0644 ${STAGING_DIR_HOST}/kernel/bzImage ${HDDDIR}/vmlinuz
+	install -m 0644 ${STAGING_KERNEL_DIR}/bzImage ${HDDDIR}/vmlinuz
 	install -m 0644 ${S}/syslinux.cfg ${HDDDIR}/syslinux.cfg
 	install -m 444 ${STAGING_LIBDIR}/syslinux/ldlinux.sys ${HDDDIR}/ldlinux.sys