meta-phosphor: prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I588025b614416c43aa2d053765ab53bacf890cb5
diff --git a/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend b/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
index e73d00f..848627a 100644
--- a/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
+++ b/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
@@ -1,4 +1,4 @@
-FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
 
 # OpenBMC loads in kernel features via other mechanisms so this check
 # in the kernel-yocto.bbclass is not required