Batch size finder is not working if batch_size is specified in LightningDataModule
🐛 Bug
The batch size finder won't work if the batch size is specified in the LightningDataModule, only (it is natural to define it there).
An instance of a LightningModule always has the attribute hparams; the batch_size finder raises a MisconfigurationException if batch_size isn't found there.
Please reproduce using the BoringModel and post here

https://colab.research.google.com/drive/1gruW3UwitVijzkhcUYIzHlIpoIB1shzt?usp=sharing
Expected behavior
Batch size finder works.
Environment

CUDA:

GPU:

Tesla T4


available:         True
version:           10.1


Packages:

numpy:             1.18.5
pyTorch_debug:     False
pyTorch_version:   1.6.0+cu101
pytorch-lightning: 0.10.0
tqdm:              4.41.1


System:

OS:                Linux
architecture:

64bit



processor:         x86_64
python:            3.6.9
version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020