meta-phosphor: prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I588025b614416c43aa2d053765ab53bacf890cb5
diff --git a/meta-phosphor/aspeed-layer/recipes-bsp/u-boot/u-boot-aspeed_%.bbappend b/meta-phosphor/aspeed-layer/recipes-bsp/u-boot/u-boot-aspeed_%.bbappend
index 6c68494..452ef7e 100644
--- a/meta-phosphor/aspeed-layer/recipes-bsp/u-boot/u-boot-aspeed_%.bbappend
+++ b/meta-phosphor/aspeed-layer/recipes-bsp/u-boot/u-boot-aspeed_%.bbappend
@@ -1,3 +1,3 @@
-FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
+FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
 
 require u-boot-aspeed.inc