[Fix] Fix a wrong paramter of `get_root_logger` in `apis/train.py`. (#486)

The get_root_logger(log_file=None, log_level=logging.INFO) function does not needs the string type cfg.log_level as input. This bug does not have negative effect.

mmcls/apis/train.py

@@ -56,7 +56,7 @@ def train_model(model,
                 timestamp=None,
                 device='cuda',
                 meta=None):
-    logger = get_root_logger(cfg.log_level)
+    logger = get_root_logger()
 
     # prepare data loaders
     dataset = dataset if isinstance(dataset, (list, tuple)) else [dataset]