meta-nuvoton: fix build warning for this layer

There is build warning as below:
WARNING: No bb files in default matched BBFILE_PATTERN_nuvoton-layer ''

Sync from templates/layer.conf rule to fix this kind of warning.
BBFILE_PATTERN_{layerid} = "^${{LAYERDIR}}/"

Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: I6a69f8f35cc7d129d605ee1f7d2519c32af53ab1
diff --git a/meta-nuvoton/conf/layer.conf b/meta-nuvoton/conf/layer.conf
index 90c5b53..22e1dc2 100644
--- a/meta-nuvoton/conf/layer.conf
+++ b/meta-nuvoton/conf/layer.conf
@@ -5,7 +5,7 @@
             ${LAYERDIR}/recipes-*/*/*.bbappend"
 
 BBFILE_COLLECTIONS += "nuvoton-layer"
-BBFILE_PATTERN_nuvoton-layer = ""
+BBFILE_PATTERN_nuvoton-layer := "^${LAYERDIR}/"
 LAYERVERSION_nuvoton-layer = "1"
 LAYERSERIES_COMPAT_nuvoton-layer = "langdale mickledore"
 LAYERDEPENDS_nuvoton-layer:append:npcm8xx = " meta-arm"