Fix docs typo: train_batch => val_batch (#4659)

Co-authored-by: Jeff Yang <[email protected]>
Co-authored-by: Jirka Borovec <[email protected]>

Author: 3 people

pytorch_lightning/core/lightning.py

@@ -599,7 +599,7 @@ def validation_step(self, *args, **kwargs):
             # the pseudocode for these calls
             val_outs = []
             for val_batch in val_data:
-                out = validation_step(train_batch)
+                out = validation_step(val_batch)
                 val_outs.append(out)
                 validation_epoch_end(val_outs)