meta-phosphor: prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I588025b614416c43aa2d053765ab53bacf890cb5
diff --git a/meta-phosphor/recipes-support/boost-url/boost-url_%.bbappend b/meta-phosphor/recipes-support/boost-url/boost-url_%.bbappend
index 5ef4f9f..618170e 100644
--- a/meta-phosphor/recipes-support/boost-url/boost-url_%.bbappend
+++ b/meta-phosphor/recipes-support/boost-url/boost-url_%.bbappend
@@ -1 +1 @@
-EXTRA_OECMAKE_append_openbmc-phosphor = "-DBOOST_URL_STANDALONE=ON"
+EXTRA_OECMAKE:append:openbmc-phosphor = "-DBOOST_URL_STANDALONE=ON"