meta-phosphor: nuvoton-layer: postd: only set SNOOP_DEVICE for npcm7xx

This allows non-Nuvoton devices to build successfully, even if the
Nuvoton layer is enabled.

Change-Id: Ie68b5737b79fbfbc18811298c450b224096d0a7b
Signed-off-by: Benjamin Fair <benjaminfair@google.com>
diff --git a/nuvoton-layer/recipes-phosphor/host/phosphor-host-postd_%.bbappend b/nuvoton-layer/recipes-phosphor/host/phosphor-host-postd_%.bbappend
index 60d5610..9999085 100644
--- a/nuvoton-layer/recipes-phosphor/host/phosphor-host-postd_%.bbappend
+++ b/nuvoton-layer/recipes-phosphor/host/phosphor-host-postd_%.bbappend
@@ -1,3 +1 @@
-FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
-
-SNOOP_DEVICE = "npcm7xx-lpc-bpc0"
+SNOOP_DEVICE_npcm7xx = "npcm7xx-lpc-bpc0"