meta-openpower: prep for new override syntax

Change-Id: I5ca16c6fa7bc616bfa9bc41c4f86d32fd92b0287
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meta-openpower/recipes-phosphor/interfaces/bmcweb_%.bbappend b/meta-openpower/recipes-phosphor/interfaces/bmcweb_%.bbappend
index 1220c8e..7390574 100644
--- a/meta-openpower/recipes-phosphor/interfaces/bmcweb_%.bbappend
+++ b/meta-openpower/recipes-phosphor/interfaces/bmcweb_%.bbappend
@@ -1,4 +1,4 @@
-EXTRA_OEMESON_append_df-openpower = " \
+EXTRA_OEMESON:append:df-openpower = " \
     -Dredfish-dbus-log=enabled \
     -Dhttp-body-limit=400 \
     "