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-bsp/skiboot/gard_git.bb b/meta-openpower/recipes-bsp/skiboot/gard_git.bb
index 214e905..49d8660 100644
--- a/meta-openpower/recipes-bsp/skiboot/gard_git.bb
+++ b/meta-openpower/recipes-bsp/skiboot/gard_git.bb
@@ -2,4 +2,4 @@
 DESCRIPTION = "gard record tool for OpenPower machines"
 
 require skiboot.inc
-EXTRA_OEMAKE_append = " PFLASH_VERSION=${PV} GARD_VERSION=${PV}"
+EXTRA_OEMAKE:append = " PFLASH_VERSION=${PV} GARD_VERSION=${PV}"