make dt_binding_check broken by drm & lvds-codec

["Rafał Miłecki" <zajec5@gmail.com>]

Hi,

I just noticed that "make dt_binding_check" doesn't work in linux-next:

   SCHEMA  Documentation/devicetree/bindings/processed-schema-examples.json
Traceback (most recent call last):
   File "/home/rmilecki/.local/bin/dt-mk-schema", line 38, in <module>
     schemas = dtschema.process_schemas(args.schemas, core_schema=(not args.useronly))
   File "/home/rmilecki/.local/lib/python3.6/site-packages/dtschema/lib.py", line 587, in process_schemas
     sch = process_schema(os.path.abspath(filename))
   File "/home/rmilecki/.local/lib/python3.6/site-packages/dtschema/lib.py", line 561, in process_schema
     schema = load_schema(filename)
   File "/home/rmilecki/.local/lib/python3.6/site-packages/dtschema/lib.py", line 126, in load_schema
     return do_load(os.path.join(schema_basedir, schema))
   File "/home/rmilecki/.local/lib/python3.6/site-packages/dtschema/lib.py", line 112, in do_load
     return yaml.load(tmp)
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/main.py", line 343, in load
     return constructor.get_single_data()
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 113, in get_single_data
     return self.construct_document(node)
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 123, in construct_document
     for _dummy in generator:
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 723, in construct_yaml_map
     value = self.construct_mapping(node)
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 440, in construct_mapping
     return BaseConstructor.construct_mapping(self, node, deep=deep)
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 257, in construct_mapping
     if self.check_mapping_key(node, key_node, mapping, key, value):
   File "/usr/lib/python3.6/site-packages/ruamel/yaml/constructor.py", line 295, in check_mapping_key
     raise DuplicateKeyError(*args)
ruamel.yaml.constructor.DuplicateKeyError: while constructing a mapping
   in "<unicode string>", line 4, column 1
found duplicate key "if" with value "{}" (original value: "{}")
   in "<unicode string>", line 113, column 1

It's caused by two commits:
ba3e86789eaf ("dt-bindings: display: bridge: lvds-codec: Document LVDS data mapping select")
d7df3948eb49 ("dt-bindings: display: bridge: lvds-codec: Document pixel data sampling edge select")

Both commits add "if" and "then" at YAML "root" level.

Can you take a look at that, please?