[Fix] Fix batch size of val_dataloader to 1.

configs/_base_/datasets/ade20k.py

configs/_base_/datasets/ade20k_640x640.py

configs/_base_/datasets/chase_db1.py

configs/_base_/datasets/cityscapes.py

configs/_base_/datasets/coco-stuff10k.py

configs/_base_/datasets/coco-stuff164k.py

configs/_base_/datasets/drive.py

configs/_base_/datasets/hrf.py

configs/_base_/datasets/isaid.py

configs/_base_/datasets/loveda.py

configs/_base_/datasets/pascal_context.py

configs/_base_/datasets/pascal_context_59.py

configs/_base_/datasets/pascal_voc12.py

configs/_base_/datasets/potsdam.py

configs/_base_/datasets/stare.py

configs/_base_/datasets/vaihingen.py

configs/beit/upernet_beit-base_640x640_160k_ade20k_ms.py

configs/beit/upernet_beit-base_8x2_640x640_160k_ade20k.py

...enetv1_r101-d32_lr5e-3_4x4_512x512_160k_coco-stuff164k.py

...enetv1/bisenetv1_r18-d32_4x4_1024x1024_160k_cityscapes.py