ipmi: fix broken asset tag function

The Asset Tag command was implemented via
https://github.com/openbmc/openbmc/commit/8af3309b, but broke via
https://github.com/openbmc/openbmc/commit/b1009126. The latter commit
did do the right thing though, the former commit had to use an append
operator instead of a weak default value, when specifying a value other
than "". The weak default value will not be set at all, when a
previously assigned value is found.

Resolves openbmc/openbmc#2867.

Change-Id: Iddfff7d894e587875898777e3ab272d55654f833
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/meta-phosphor/common/recipes-phosphor/inventory/phosphor-inventory-manager-config-native.bb b/meta-phosphor/common/recipes-phosphor/inventory/phosphor-inventory-manager-config-native.bb
index d7dd57e..0b1c453 100644
--- a/meta-phosphor/common/recipes-phosphor/inventory/phosphor-inventory-manager-config-native.bb
+++ b/meta-phosphor/common/recipes-phosphor/inventory/phosphor-inventory-manager-config-native.bb
@@ -7,7 +7,7 @@
 inherit obmc-phosphor-license
 inherit native
 
-PHOSPHOR_INVENTORY_MANAGER_CONFIGS ??= "phosphor-inventory-manager-assettag-native"
+PHOSPHOR_INVENTORY_MANAGER_CONFIGS += "phosphor-inventory-manager-assettag-native"
 
 # To add additional managed inventory items, create a recipe in your layer,
 # and add it to PHOSPHOR_INVENTORY_MANAGER_CONFIGS with a bbappend to this recipe.