dt-bindings: vendor-prefixes: Also allow node names starting with '_'

Generated nodes for overlays begin with '_'. The binding examples are
built as overlays in order to allow unresolved phandles, so we need to
allow the generated node names.
Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.yaml

@@ -1028,7 +1028,7 @@ patternProperties:
 
   # Normal property name match without a comma
   # These should catch all node/property names without a prefix
-  "^[a-zA-Z0-9#][a-zA-Z0-9+\\-._@]{0,63}$": true
+  "^[a-zA-Z0-9#_][a-zA-Z0-9+\\-._@]{0,63}$": true
   "^[a-zA-Z0-9+\\-._]*@[0-9a-zA-Z,]*$": true
   "^#.*": true