[Fix]: fix coco registry problem (#1536)

mmdet3d/datasets/builder.py

@@ -3,6 +3,7 @@ import platform
 
 from mmcv.utils import Registry, build_from_cfg
 
+from mmdet.datasets import DATASETS as MMDET_DATASETS
 from mmdet.datasets.builder import _concat_dataset
 
 if platform.system() != 'Windows':
@@ -39,7 +40,8 @@ def build_dataset(cfg, default_args=None):
         dataset = CBGSDataset(build_dataset(cfg['dataset'], default_args))
     elif isinstance(cfg.get('ann_file'), (list, tuple)):
         dataset = _concat_dataset(cfg, default_args)
-    else:
+    elif cfg['type'] in DATASETS._module_dict.keys():
         dataset = build_from_cfg(cfg, DATASETS, default_args)
-
+    else:
+        dataset = build_from_cfg(cfg, MMDET_DATASETS, default_args)
     return dataset