[Fix] Fix wrong links of .pth and .json file in DMNet and UNet(FCN) README.md

[MengzhangLI]

Fix wrong links of .pth and .json file of DMNet and UNet(FCN) in ./configs/ folder.

Just as two related issues which reflect unsuccessful link of DMNet (#548) and UNet drive FCN S5-D16 (#415), we fix the correct link of those models.

Best,

[codecov]

Codecov Report

Merging #660 (747e342) into master (170a9d1) will decrease coverage by 0.64%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #660      +/-   ##
==========================================
- Coverage   85.82%   85.17%   -0.65%     
==========================================
  Files         103      105       +2     
  Lines        5304     5668     +364     
  Branches      856      923      +67     
==========================================
+ Hits         4552     4828     +276     
- Misses        581      662      +81     
- Partials      171      178       +7     

Flag	Coverage Δ
unittests	85.16% <ø> (-0.65%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmseg/models/backbones/vit.py	84.84% <0.00%> (-1.03%)	⬇️
mmseg/models/utils/__init__.py	100.00% <0.00%> (ø)
mmseg/models/backbones/__init__.py	100.00% <0.00%> (ø)
mmseg/models/necks/multilevel_neck.py	100.00% <0.00%> (ø)
mmseg/models/utils/timm_convert.py
mmseg/models/utils/embed.py	80.55% <0.00%> (ø)
mmseg/models/utils/ckpt_convert.py	4.28% <0.00%> (ø)
mmseg/models/backbones/swin.py	86.89% <0.00%> (ø)

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[Junjun2016]

Hi @MengzhangLI
Could you please test several models