populate quantization_config for kv-cache-scheme only configs (huggin…

…gface#33874)

src/transformers/utils/quantization_config.py

@@ -1105,7 +1105,7 @@ def __init__(
         self.sparsity_config = None
 
         # parse from dict to load nested QuantizationScheme objects
-        if config_groups:
+        if config_groups or kv_cache_scheme:
             self.quantization_config = QuantizationConfig.parse_obj(
                 {
                     "config_groups": config_groups,