meta-google: os-release: Avoid effect not gbmc distro

Add distro override to avoid os-release setting effect other
not gbmc distro

Signed-off-by: Brian Ma <chma0@nuvoton.com>
Change-Id: I34afb4ce8e72f2be15a5f5668e6ff6c567548ad5
diff --git a/meta-google/recipes-core/os-release/os-release.bbappend b/meta-google/recipes-core/os-release/os-release.bbappend
index f6b7cc1..635f7c5 100644
--- a/meta-google/recipes-core/os-release/os-release.bbappend
+++ b/meta-google/recipes-core/os-release/os-release.bbappend
@@ -8,4 +8,4 @@
 }
 
 IMAGE_TYPE = "${GBMC_CONFIG}"
-OS_RELEASE_FIELDS:append = " BUILD_MEMO IMAGE_TYPE"
+OS_RELEASE_FIELDS:append:gbmc = " BUILD_MEMO IMAGE_TYPE"