meta-ibm: prep for new override syntax

Change-Id: I9116ed7260e369136acb39eec15075db2d4dbeba
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meta-ibm/meta-palmetto/recipes-phosphor/images/obmc-phosphor-image.bbappend b/meta-ibm/meta-palmetto/recipes-phosphor/images/obmc-phosphor-image.bbappend
index 7553460..6e76d4a 100644
--- a/meta-ibm/meta-palmetto/recipes-phosphor/images/obmc-phosphor-image.bbappend
+++ b/meta-ibm/meta-palmetto/recipes-phosphor/images/obmc-phosphor-image.bbappend
@@ -1 +1 @@
-OBMC_IMAGE_EXTRA_INSTALL_append_palmetto = " mboxd"
+OBMC_IMAGE_EXTRA_INSTALL:append:palmetto = " mboxd"