schema: Use draft7 meta-schema (again)

When splitting the schema and validator classes, we inadvertently switched
from draft7 meta-schema to draft2019-09 meta-schema which doesn't fully
work due to incomplete $recursiveRef support in jsonschema module. That's
now fixed, but only in newer versions we don't yet support.

Signed-off-by: Rob Herring <robh@kernel.org>

dtschema/schema.py

@@ -132,7 +132,9 @@ def is_valid(self, strict=False):
             for error in self.iter_errors():
                 raise error
         else:
-            for error in self.DtValidator(self.DtValidator.META_SCHEMA).iter_errors(self):
+            # Using the draft7 metaschema because 2019-09 with $recursiveRef seems broken
+            # Probably fixed with referencing library
+            for error in self.DtValidator(jsonschema.Draft7Validator.META_SCHEMA).iter_errors(self):
                 scherr = jsonschema.exceptions.SchemaError.create_from(error)
                 raise scherr