fix bug of block.AbstractInput

[fangwei123456]

Issue Number:

Objective of pull request:

Pull request checklist

Your PR fulfills the following requirements:

• Issue created that explains the change and why it's needed
• Tests are part of the PR (for bug fixes / features)
• Docs reviewed and added / updated if needed (for bug fixes / features)
• PR conforms to Coding Conventions
• PR applys BSD 3-clause or LGPL2.1+ Licenses to all code files
• Lint (flakeheaven lint src/lava tests/) and (bandit -r src/lava/.) pass locally
• Build tests (pytest) passes locally

Pull request type

Please check your PR type:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation changes
• Other (please describe):

What is the current behavior?

Traceback (most recent call last):
  File "/home/wfang/spikingjelly_dev/spikingjelly/test.py", line 6, in <module>
    print(net(torch.rand([1, 2, 3])))
  File "/home/wfang/anaconda3/envs/lava-env/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1130, in _call_impl
    return forward_call(*input, **kwargs)
  File "/home/wfang/anaconda3/envs/lava-env/lib/python3.10/site-packages/lava/lib/dl/slayer/block/base.py", line 94, in forward
    self.input_shape = input.shape[1:-1]
AttributeError: 'builtin_function_or_method' object has no attribute 'shape'

What is the new behavior?

No errors.

Does this introduce a breaking change?

• Yes
• No

Supplemental information

Here are the minimal codes to reproduce this error:

import torch
from lava.lib.dl import slayer

net = slayer.block.cuba.Input()
print(net(torch.rand([1, 2, 3])))

[bamsumit]

@fangwei123456 Thanks for the bugfix :)