[caffe2] Fix shape inference for LpNorm (#53332)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53332
This is to make sure we don't get `BATCH` dim type for the output.
Reviewed By: ChunliF
Differential Revision: D26836902
fbshipit-source-id: bedbd12330c608406e3466b240015235a28d2c4a
