neck网络ChannelMapper导出out_shape出错

[Yang-Changhui]

问题确认 Search before asking

• 我已经查询历史issue，没有发现相似的bug。I have searched the issues and found no similar bug report.

Bug组件 Bug Component

No response

Bug描述 Describe the Bug

使用neck网络为ChannelMapper，使用以下命令创建neck = cfg['neck'] and create(cfg['neck'], **kwargs)，
得到neck.out_shape报错，原因：ChannelMapper中out_shape函数没有self.spatial_scales

复现环境 Environment

os:linux
paddle:develop
paddledetection:develop

Bug描述确认 Bug description confirmation

• 我确认已经提供了Bug复现步骤、代码改动说明、以及环境信息，确认问题是可以复现的。I confirm that the bug replication steps, code change instructions, and environment information have been provided, and the problem can be reproduced.

是否愿意提交PR？ Are you willing to submit a PR?

• 我愿意提交PR！I'd like to help by submitting a PR!