meta-facebook: more prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I21120d6215c25be49afd60d6e807b68f2798423a
diff --git a/meta-facebook/conf/machine/include/facebook-withhost.inc b/meta-facebook/conf/machine/include/facebook-withhost.inc
index dba7444..ebe79d1 100644
--- a/meta-facebook/conf/machine/include/facebook-withhost.inc
+++ b/meta-facebook/conf/machine/include/facebook-withhost.inc
@@ -10,6 +10,6 @@
 VIRTUAL-RUNTIME_obmc-host-state-manager ?= "x86-power-control"
 VIRTUAL-RUNTIME_obmc-chassis-state-manager ?= "x86-power-control"
 
-PREFERRED_PROVIDER:virtual/obmc-host-ipmi-hw ?= "phosphor-ipmi-kcs"
+PREFERRED_PROVIDER_virtual/obmc-host-ipmi-hw ?= "phosphor-ipmi-kcs"
 
 OVERRIDES .= ":fb-withhost"