qapi/expr: Enforce feature naming rules again

Commit e42648dc "qapi/expr.py: Remove single-letter variable"
accidentally removed the check for "only lower case letters and
hyphens".  Restore it.

Fixes: e42648dc
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220510061645.3209195-2-armbru@redhat.com>

scripts/qapi/expr.py

@@ -443,7 +443,7 @@ def check_features(features: Optional[object],
         check_keys(feat, info, source, ['name'], ['if'])
         check_name_is_str(feat['name'], info, source)
         source = "%s '%s'" % (source, feat['name'])
-        check_name_str(feat['name'], info, source)
+        check_name_lower(feat['name'], info, source)
         check_if(feat, info, source)