[Fix] Fix get_flops scrip (#3551)

## Motivation

`inputs` and `input_shape` can't be both set to mmengine api
`get_model_complexity_info`

open-mmlab/mmengine#1056


## Modification

Set `input_shape` to None.

tools/analysis_tools/get_flops.py

@@ -86,7 +86,7 @@ def inference(args: argparse.Namespace, logger: MMLogger) -> dict:
  'supported yet.')
  outputs = get_model_complexity_info(
  model,
- input_shape,
+ input_shape=None,
  inputs=data['inputs'],
  show_table=False,
  show_arch=False)