meta-phosphor: prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I588025b614416c43aa2d053765ab53bacf890cb5
diff --git a/meta-phosphor/raspberrypi/recipes-kernel/linux/linux-raspberrypi_%.bbappend b/meta-phosphor/raspberrypi/recipes-kernel/linux/linux-raspberrypi_%.bbappend
index 72d991c..4fc41d0 100644
--- a/meta-phosphor/raspberrypi/recipes-kernel/linux/linux-raspberrypi_%.bbappend
+++ b/meta-phosphor/raspberrypi/recipes-kernel/linux/linux-raspberrypi_%.bbappend
@@ -1 +1 @@
-FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"