Fix bmcweb append in openpower

Tested:
Booted up Romulus in QEMU and verified the following:
- bmcweb started without error
- Redfish command to view dbus event logs worked

(From meta-openpower rev: 3169d777af83bc2e8ede83d28168c20155924d2a)

Change-Id: I03828b46b83721e7e63d2a2670c113ffd08a51ce
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-openpower/recipes-phosphor/bmcweb/bmcweb_%.bbappend b/meta-openpower/recipes-phosphor/bmcweb/bmcweb_%.bbappend
index 0765ddf..1035bf1 100644
--- a/meta-openpower/recipes-phosphor/bmcweb/bmcweb_%.bbappend
+++ b/meta-openpower/recipes-phosphor/bmcweb/bmcweb_%.bbappend
@@ -1 +1 @@
-EXTRA_OECMAKE_df-openpower += "-DBMCWEB_ENABLE_REDFISH_DBUS_LOG_ENTRIES=ON"
+EXTRA_OECMAKE_append_df-openpower = " -DBMCWEB_ENABLE_REDFISH_DBUS_LOG_ENTRIES=ON"